[swarmee]

Much cheaper fees than ones being graded. Retains the cert number, so you can tell it's still an older grade though.
They used to reholder when you paid for a review (if you asked nicely), but they quit doing that a few years back. Cards reholdered at some levels now also get scanned and those images loaded onto psacard.com as part of the fee as well.

Plenty of reasons why people don't: expense, time lag, possibility of PSA saying the holder is cracked and has to be regraded. Some would also be worried about it getting damaged in PSA's hands or lost in the mail.

Add: very rare that PSA would downgrade a card during a reholder submission, it would have to be drastic like they see evidence of alteration, writing that didn't get a mark, or was actually counterfeit. But they'd also have to pay out on the grade guarantee.