I can only speak for cishet dynamics - the most commonly cited reason and I guess most obvious reason is that dudes are thirsty for younger women, but ime the reverse is also often true, either because they've found men in their age bracket to be lacking in some way (take yr pick), or because they have some idea that older men will have their shit more together. (I can confirm this is generally NOT the case but anyway.)

There's so little social pressure for cishet men to mature that it sometimes feels like you gotta age up your demographic to find someone who isn't a manchild

And even that isn't a guarantee lol, 45 year olds who have never cleaned a toilet or reflected on anyone else's interiority.