To give an analogy - people are well aware that shopping centre spaces are private...not public. You haven't got a right to be there...there's been all sorts of free speech issues. Private spaces can just bar you - like I was barred off FB. Sadly.
People could meet at a free park or open public space - but it might not be convenient, might be raining, might be closer, etc.
So people go to the mall/shopping centre - very soulless places IMO - and talk there. Is it better? No. But it's a place to meet.
Most social media is likewise. Unless it literally is on fire like Twitter, most people will put up with a lot of shit cos others they know are there. Massive lock in....people use WhatsApp but not Signal or Telegram. People use text which is very insecure. It's whatever is easiest...not necessarily the best.
And if you said 'hey I know this free park over here' and it's cold/wet/not near...your friends or family will likely leave you to it and stay in the shopping centre.