I mainly blame Facebook for this, but these days it's now viewed as seedy and odd to try and be friends with strangers across the internet. Each new 'social service' that now appears is not only silo-ed by it's own protocol, but also promotes the continued siloing of users into their own (existing) friendship groups.

Back in the day (yeah, I'm old), you could drop into an IRC channel of strangers and be having a good conversation within minutes[1]. ICQ, as mentioned, had a 'find friend' feature, and many other early social platforms encouraged like-minded strangers to interact.

So we all end up just talking to the same 20 or people we've always spoken to, re-enforcing the echo-chamber-effect, and never introducing new ideas and viewpoints into our lives.

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[1] IRC these days, if you are lucky to find an active channel, is now so cliquéy that any interlopers are largely ignored.