Why would they be? If I mail you a bunch of pictures in an envelope, they don't magically convert to negatives and transfer themselves to the roll of film inside your analog camera.
<rant>
Snark aside, "camera roll" must be one of the most confusing attempts at "user-friendly" abstractions I've seen in widely-deployed software, especially with so many apps shipping their own implementations (in addition to the OS/camera gallery), some of which mix together some combination of pictures downloaded to (but not taken by) the phone, pictures existing only in the cloud, pictures existing only in a different app's cloud...
There's skeuomorphism, and there's building a bad abstraction on top of a limitation of ancient tech, seemingly forgetting the ~10+ year period between analog cameras and smartphones with good imaging sensors, where everyone got used to digital cameras shooting photos to a "memory card". My non-tech-savvy relatives are definitely more confused about "camera rolls" in their phones than they were about managing JPGs on SD cards using standard desktop OS filesystem tools.
Hell, number one support request I get from family these days is, "How do I copy ${these photos from a "camera roll" of some app} to ${OS gallery app} and to ${this USB stick}? We want to show all photos of ${grandchild} to ${neighbor} without Internet. And we want to have them in ${a folder on a PC} so it's safe, and we can view it on a large screen." The process isn't that involved, just confusing, and somewhat different for every other app. It's like vendors really don't want people to store their photos as files anymore :).
</rant>
Because they were saved to the central photo place with WhatsApp, and she likes seeing all of her photos there.
In case you haven't noticed, there seems to be an active effort to do away with the notion of files. Because making things more abstract is supposed to reduce confusion somehow.
You can do whatever you want with a bunch of bits and a spec that tells you what they mean. Even utilize different software/hardware to consume and manipulate them, which is the last thing your software/hardware vendor wants you to do.
Did anyone really think doing away with files ever had anything to do with simplicity? Another magical thing you can do with a bunch of bits is build abstractions over them to simplify their manipulations as much as you want. It's vendor lock-in and it's not only awful but evil too.
Result is they can't find them, lose them, don't have backups etc. I have interacted with users who hadn't grasped before they could make folders themselves.
Ask your mother or your sister.
But unfortunately, vendors have caught up and noticed that "an arm and a leg" is lots of money, so if they could just make it a tiny bit harder...
Me being able to freely manipulate my own data according to my capacity has NOTHING to do with providing uninterested/incapable people with tools that hide complexity.
Mine can work with files just fine. They teach this stuff in schools over here.
It might not be the "best" way but I'm not sure there is one. Instead of browsing content by type ("all photos") and scrolling until she finds what she wants, she browses by context ("all stuff involving family") and scrolls until she finds photos. She is not totally comfortable with the idea that a photo is a bunch of bytes that can be read from multiple places. She prefers going back to the place the content comes from, because that's just easier.
Of course one way is better in some situations, and the other is better in others. But not putting photos in the camera roll has one advantage: it doesn't store them in a storage that's probably unencrypted and readable offline by someone with physical access
I took a similar tack over malware & backups some years ago. I was spending far too much time being family tech support in "oh shit" moments, trying to remove crap from people's laptops and other, then (when I gave up doing it that way) hunting down all their files and backing them up before hosing and reinstalling the OS, hunting out the correct drivers, and each time giving advice on keeping backups, avoiding malware, telling them that they must keep any driver discs (or generate them from the machine) when they get a new device so they can be identified & reinstalled later, etc, each time being completely ignored because once things were restored they completely forgot the issue. Once I stopped rolling over and being infinitely and immediately helpful, instead saying "without the backups and such I asked you to keep it might take a few hours to sort this out, I can do it for you but I probably can't fit it in for a couple of weeks" most stopped asking me to help - not because they see my time as having value or because they've started to get less dim about letting malware in, but because I'm seen as grumpy and unhelpful.
I was able to get grandma on Signal precisely because it was the little secret between us. She knew that a signal coming in was from me, and only me. I was using it to talk to her. And she thought it was cool that we talked via signal to her before any other family member caught on the signal craze.
I was able to get my SO to use signal on the same principle. Pick the people in your life that care about you - and care back. You are available via signal, while you ingnore whatsapp et al. You answer right away on signal whereas on other stuff, you wait.
Its funny how far along you can take a feature-lacking app provided its simple for others to use, and there is an emotional attachment in its use.
I just told her to dowload the app.
At its core, signal is still a messenger app. Its not hard to use. I dont think you realize how powerful are simple things like "good morning" and "i love you" to your family and loved ones. Give a little of it, and see the results.
In the local and direct sense, it is no worse for grandma, and that is the point everyone is arguing. It will work for her use case while also being better in the global sense.
I'm also a privacy advocate, but there are downsides that you need to acknowledge.
I would however have trouble with the implication that having this stance is the consequence of being in an idealistic bubble, though perhaps you did not mean that.