As mentioned in the article, pi-hole complements a browser ad block, doesn't replace it.
My wife likes to cast youtube videos from her phone to the TV, so the experience is nearly the same to her on her phone as it is watching on TV. Maybe if she only used the PC interface she wouldn't mind, but she likes to search / scan / scroll youtube on her phone, and cast the bits she's going to actually watch.
She was very frustrated by having to find the video she wanted to watch on her phone on the PC using the some what finicky mouse touch pad to get the cursor to open the web browser, navigate to youtube, enter the title in the search box (possibly) scroll to find the video, and then a couple more steps getting it playing full screen.
I'm happy we have options to block ads that aren't uBlock Origin in firefox, even though that works great, and better than other options.
My best guess at why people don't want to do this is that we're conditioned not to do anything that isn't advertised to us, and nobody is running adverts telling you to hook a laptop up to your TV for a superior smart TV experience.
But I also get why people just want to sit on the couch, find a nice video on the phone and with the press of a button want to see it on the TV. No computer boot time, no updates, no writing on the keyboard while laying down.
I get that you can buy a fanless pc, install linux with unattended-upgrades and you have something more powerful. But most people don't know how or don't want to go through that hassle.
Again, for you yes. But some lay down on the couch and a keyboard in that posture is just annoying.
And copying a youtube video from the app, into firefox app to just send it to the computer is bonkers complicated when you could just press the cast icon.
A lot of people interact with their phone all the time, but rarely use the computer. I'm telling you, it's more easy to use the build in Youtube app for a lot of people.