If I remember your age correctly, you’re not old enough to make a sweeping statement like that. Do you even remember the pre-internet era?Meh. People have lived in echo chambers for decades, we just have better data on it now. I'm totally off social media at the moment but I still live in an echo chamber of left wing media - the Guardian in the UK, the Atlantic for world news, New Yorker and MSNBC for US news. There are loads of people who have been reading the same newspapers and having the same conversations among the same group of friends for decades. We're creatures of habits who love nothing more than being told what we think and how we feel is correct.
I'm not saying that social media hasn't changed anything but the contrast to other media really is not that stark. You'd think everyone was wonderfully informed and balanced 50 years ago! The reality is people lived in much smaller bubbles then, and the bubbles were created by much more worrying social constructs. There were undoubtedly much fewer of those bubbles and there was less polarisation, but the fundamental issues were still very much there.
Yes people have always bought newspapers that conform to their pre-existing political views, and people naturally socialize with likeminded people. The difference is that with the mass explosion in cable TV offering vastly more choice for partisan news sources, and more importantly the new social media phenomena where people are seeing a constant barrage of extremely partisan propaganda, they don’t have a reasonably unbiased arbitrator of what is real or not. In the past people might read the Guardian or the Sun but they were almost without fail also seeing one of the mainstream TV news shows like the BBC which provided a stabilizing influence. Now we see people denying the reality of those sources in a way we just didn’t see before. ‘Fake News’ wasn’t a Trump invention, it has been a slow and steady delusion that the internet has played its part in spreading. Now we’re seeing the previously neutral internet trusted fact sources like Snopes come under heavy attack too, largely based on social media attack campaigns intended to undermine their reputations to allow the flow of disinformation to spread even more freely. We’re literally living in a time where a majority of people can believe things that would once have been the preserve of extremist whackjob conspiracy theorists, and that is massively the fault of social media (reinforced by cable TV).