We get a lot of generic fighters (the chassis) in our games.Because of the basic concept.
That's it.
Just like people want a magical warrior type, but don't have it, a lot of other people want a character whose primary deal is that they're a skilled warrior, in armour, probably with a sword of some kind. I will say it seems to rather less popular with younger players than older, in my experience anyway. Whereas say, Rogue is as popular as it ever was.
I feel they are still as popular, and find their "generic" nature helps build a wide spectrum of archetypes.
Anecdotally of course...