Because buy doesn't exist in a sane form for some things. Kids shows are known for never selling by season and only by some weird theme and of course there are dupes between sets. Buy isn't an option at all for some stuff. I'm looking at you Disney vault bulkshit, but also other not as iconic stuff.

Yes pirate, but that's a problem too. I've tried to pirate some stuff that wasn't popular or it was too old and you're just not able to.

Streaming removes a lot of that hassle. Now that the price is becoming too high, people are considering other options, but there is a reason it exists. Streaming is how I let my kids explore media. Yes, I can just give them my childhood favs, but they need a way to try new shows without me directly interfering and it's been great. I would have never picked out my kid's favs for her.