If I'm wearing jeans it's generally because I'm doing something active, grubby & potentially sweaty, so they're usually ready for the wash once I take them off. Although if I've got another grubby, sweaty day lined up, I'll save them for that & wear them again.
My crotch is showered daily, & encased in nice clean cotton knickers, thank you very much, but my jeans still definitely get slightly stale smelling after a few wears, especially if they're skinnies.
If you really can't wash expensive jeans, then I'm glad that all mine are cheap or second hand.
My current favourite pair for scruffing around in are handed down from teenage ds. They're quite baggy so don't need washing because of sweating etc in the same way as a tight pair of skinny jeans would - but then I usually manage to cover them with sand, dust, oil, animal hair.They seem to survive the washing machine perfectly well, given that they had at least a year of ds testing them to destruction before I rescued them from the recycling.