>I don't think it's ominous. Different platforms serve different interests and demographics

Split into two separate social networks dramatically increases the echo chamber effect.

e.g. on reddit someone from /r/conservatives might still interact with /r/liberals because they both have an interest in /r/succulents

They may not be speaking about politics but they're still interacting. If you're on two different platforms even that minor overlap falls away & that allows for the two to drift further apart and harden in their views