Vintage computer meetups, like vintage car meetups, are mostly chummy in-group gatherings for the already initiated. It's where geeks of a particular brand can talk shop. (I usually don't attend them and instead go to demo parties[1], which are in no way any less esoteric.)
> There wasn’t really much for newcomers to explain why this old hardware deserves preservation.
It does and doesn't - much like old cars, record players, fighter jets, trains, radios and phones. A handful can be kept around for posterity, as museum pieces. There's a point in not forgetting how they work, since most modern stuff is to a large extent refinements and complexity layered on top of previous knowledge.
But mostly, it's just a fringe hobby. Old computers deserve preservation because someone cares deeply about them and loves tinkering with them. Just like with old cars, record players, trains and radios.
[1] https://en.wikipedia.org/wiki/Demoscene