I'm late 30s, and formal dancing like this isn't something I'm into or have any close friends who are into - so this isn't something that's just happened suddenly with your generation. I don't think my parents know how to dance in any formal way either. This isn't some sudden loss of culture.
Most of the Western weddings I've gone to have a 'first dance' (where often the couple may have taken some lessons beforehand and which will therefore be more formal) but then after that the band or DJ will play pop/rock/hip-hop/disco music and everyone else will dance along to that. But that's dancing in the sense of how the vast majority of people (who have never taken lessons) know how to dance - i.e. the informal way we all learnt to dance at school discos or student parties or nightclubs - not the more structured dancing styles you're describing.
It sounds like you're quite into dancing as a hobby, given you mention having friends from swing dancing nights - but most people aren't, it's a bit of a niche. So you're disappointed that your hobby isn't more mainstream, but I wouldn't go blaming that on your fellow wedding guests. I'm quite into Star Trek, but when I go to weddings I don't grumble that the bride didn't walk down the aisle to the TNG theme.
My advice would be to accept that your hobby isn't something that most people are in to and not to judge other people for that. Instead seek out clubs and societies for people who do share you interest, where you can ballroom dance the night away together.