I posted earlier something about how when played pressed against one's abdomen, the bass guitar shakes out the nasty stuff. That's one good reason for sure.
But there's also the charm of the instrument being just about exactly as old as I am. Other modern instruments took longer to get up to being essential. The saxophone at age 73 was still largely being used to make flatulent barnyard effects (not to offend any sax players out there... it really did catch fire about then when Bechet, Bean, & Frankie Trumbauer got hold of it).
Then there's the very satisfying irony that while today our instrument is totally sine qua non, when I started on bass (1964), it wasn't in any way taken seriously as an instrument (certainly not in the public school music programs). And in R&R, extra, perhaps less adept (or perhaps less egocentric) guitarists back in '65 were encouraged to play bass because, well, someone had to do it. So that's some satisfying irony for sure.