It happened because most people don't build websites themselves, they contract the work out. And when you look for contractors who build websites, you'll find J

It happened because most people don't build websites themselves, they contract the work out. And when you look for contractors who build websites, you'll find JS developers, because that is where the lucrative work is therefore that is what developers learn. There is no pushback on it because as long as it works, people are happy and continue paying. And none of the clients test with js disabled. Devs use it because the moment the client needs something somewhat dynamic, some js will need to be included anyway so you might as well use your usual stack. Basically "why do people use js where HTML does the trick" is the same question as "why do people use python where c89 does the trick"