You're kind of wanting it both ways, to some extent.
I mean, I'm annoyed that Netflix had a bunch of Marvel movies, but not all of them. I'm annoyed that I used to watch them on Netflix all the time and now they're gone.
On the other hand, it's because Disney+ exists, and there's no reason for Disney+ to ever remove them (preasumably), since they own the rights to them so there's no licensing deals to work with. That means that they should be there "forever".
Likewise, I don't want to also have to pay for CBS All Access to watch the latest Trek, but, if I do, it does mean that I don't have to worry about Star Trek: Discovery disappearing down the road.
The only way for things to be there "forever" is to be streaming from the company that owns the copyright, and more and more such companies are setting up their streaming services and can then guarantee that "foreverness", but that comes at costs for them, and thus costs for us. It's unfortunate, but it feels as though it's either one or the other.