When I started biking I did not wash my bike shorts until I could smell my-selves.
(I did use underpants)
I also got a very bad case of "Jock Itch" which took medicine and much attention to get rid of.
Ever since I wash my bike pants with Anti Bacterial Soap and also use powder to prevent recurring this unpleasant experience. (No more underpants)
I hope this helps.
I have no Idea how these other folks can do it without special care unless there are different resistance to these bugs.