I'm not a physicist nor a person who understands physics at all, but if what you say is true, wouldn't the most likely explanation be that physicists do that specifically for fear of losing their job?
I think it's the rare physicist that actually thinks "Yes, this work is useless, but I need a job and will keep up the subterfuge." I think the rationalizations are more common. But this is just my opinion. And consider the context: what's the alternative? Do you realize how hard it is to discover something actually, really new? And the sheer impossibility of doing scientific discovery on a schedule? The expectations are really insane in science. I can't help but think that "professional scientist" is not such a good idea, that we were better off when people did science on the side, as a hobby, and once in a while they'd find something cool and publish it.
(That said: also the majority of physics research isn't fundamental physics research, which is the stuff you're talking about. There's plenty of work in areas like condensed matter physics, plasma physics, quantum optics, etc etc etc that is still producing results and driving new developments.)