Gen-Xer here: Napster was never made illegal
Napster lost several lawsuits in the US and filed for bankruptcy
But Napster the brand was sold to Roxio and continued operations
it's still active today
https://www.napster.com/
Anyway, in retrospective, Napster times were fun, university networks were clogged by students downloading music all day long and, at least in my country, many people bought a dial up internet connection just to use it.
But it had serious unexpected consequences, it gave birth to new generations of listeners that do not buy music, because they never had to, and the musicians are now paid virtually nothing for the music they create, while majors still make a lot of money, which isn't exactly what we hoped for when we hated on Metallica for suing Napster.
People were not using it because it was illegal, people were using it because it was cool. It was mostly young people.
Chats are a different beast, if they were ever made illegal, a lot of people would stop using them, because they would disappear from app stores and a prominent smartphone manufacturer we all know would probably delete the app remotely from the users' devices and report to the authorities whoever would dear to sideload it.
I feel sometimes a little bit conflicted about those years when I see my musician friends touring over and over because selling records and make a living of it it's not a thing anymore, and now I buy a lot more music than I did in the past (which was already a decent amount), directly from artists when I can.