OP, I've heard this myself. Its odd and I don't care for it either. I also notice that the hired band will often do almost as much DJ stuff (just spinning songs) vs actually playing live. It's likely that its all about getting the gig and the fact that most people at events/venues (weddings, restaurants, wineries etc.) could hardly care less about how the music is delivered, they just want to dance and have fun while hearing music performed in a familiar way. There is a sax player locally who gigs quite a bit. His thing is to play familiar songs from the past with featured sax parts (think Pink Floyd/Money, Foreigner/Urgent, Billy Joel/Just The Way You Are etc etc) while he plays over them ... or just doubles the sax parts. I call it Saxophone Karaoke. He does know how to play pretty well but I really dislike it, but I've heard non-musicians rave about the guy.
Several of my friends around the country who are still full-timers report that brides are perfectly happy with DJ and Karaoke music.
Players gotta do whats needed to get the gig and get paid I guess.