Try it for yourself. This may sound nasty, but smell all of your 'clean' polyester and nylon gym shorts.
They probably smell nasty. Unless you just bought them.
That's because you can't wash plastic (which is polyester, nylon, spandex, etc.) the way you wash cotton, or wool.
The odor-causing bacteria sticks to the plastic. Regular laundry detergent doesn't kill it (regular laundry detergent also is toxic to humans). Even enzyme-based laundry detergent won't fully kill it.
Just in case assaulting your balls with microplastics doesn't scare you enough, remember that every time you wear those gym shorts they aren't actually clean. They still smell bad and will CONTINUE to smell bad as long as you wear them
Get rid of them and invest in merino wool shorts and underwear. Merino wool is naturally odor resistant and sweat wicking. They are also comfy AF.