I used to stream all my videos 144p less than 5 years ago because streaming any higher resulted in a stuttering buffering mess. Youtube was the only streaming service I could watch because most other sites didn't bother with resolutions/bitrates so low. Maybe that's why youtube won out. Much like how whatsapp made it their mission to run on every phone they could get their hands on.

Now we have proper internet I don't but don't for a second doubt that a sizable portion of the internet still suffer from slow speeds, even those living in developed countries.