Your notion makes zero sense. Wanting to keep the money never incentivizes contact. If they wanted to keep the money, the surest way to accomplish that is to just keep it.
>Wanting to keep the money never incentivizes contact.
It could in combination with the authors' hypothesis of not wanting to view oneself as a thief. Under that condition, the likely behaviour is to simply let the wallet sit in a lost-and-found drawer. Writing the email starts the clock on a license to take it while giving yourself a rationalization.
you don't know if the wallet owner or that original person will turn up and make enquiries as to what happened, and of you just keep the money, there is a real risk your actions being discovered.
whereas at least if you TRY to return the wallet, when you do eventually keep the money, you have an angle of both plausible defense, and arguably, natural justice on your side...