For a studio musician, time is of the essence. The engineer is being paid to get a track down as quickly as possible, and telling a bass player to bring a standard bass is a courtesy that he doesn't have to extend. It has nothing to do with lazy, it has to do with time. One of the first pieces of advice a pro gives to a young session player is to always bring a couple of Fender basses to a session in case you're asked to use it, one with flats, one with rounds, etc.
I know you're speaking hypothetically, and we're just throwing things around, but if a session player decides to give the engineer crap, there are a thousand guys who will show up with the right gear, and he's going to work with those guys instead. It's less time for them to bring in someone else than to set up the board for that Wal bass on that orange juice commercial track.
All of this information I'm relaying is based on a commercial music education over 20 years ago. A smart session player will always have a Fender bass with him, but it's probably not as necessary as it may have been back in the day.