Stable is a very different word from homogeneous. It implies a regular cast of characters, not an identical one.
Late-90s to late-2010s forums were hardly all homogeneous. Age-wise was the most homogenous dimension - the number of folks 40+ was low - but many of these communities were full of people who'd grown up with the internet pre-college or even pre-high-school.
With a stable cast of characters you actually get to know people even if they're different, you don't simply assume that their interests oppose yours, like you seem to be doing.
Late-90s to late-2010s forums were hardly all homogeneous. Age-wise was the most homogenous dimension - the number of folks 40+ was low - but many of these communities were full of people who'd grown up with the internet pre-college or even pre-high-school.
With a stable cast of characters you actually get to know people even if they're different, you don't simply assume that their interests oppose yours, like you seem to be doing.