The system could be set up to automatically refund, if your PR wasn't checked for over $AVERAGE_TIME_TO_FIRST_REVIEW$ days. The variable is specific to the project, and even can be recalculated regularly and be parameterized with PR size.
I don't think you heard what I said: I don't want to pay money to contribute to someone else's project. If I fixed your bug, I'm not paying you money for you to ignore my PR for _any_ amount of time, I'm simply not going to contribute back.
Moreover, I'm not interested in having my money get handed over to folks who aren't incentivized to refund my money. In fact, they're paying processing costs on the charge, so they are disincentivized to refund me! There could be an escrow service that handles this, but now there's another party involved: I just want to fix a damn bug, not deal with this shit.