Why don't bug reporting systems provide workarounds as rewards to users?

That would basically be customer support, and after a certain point companies start adding friction and reducing costs in actual human customer support.

With small companies you can do that, usually bug reports can be sent through email directly to a person that will review it, and you can just ask for a workaround once it is available. That won't work with bigger companies, though, unless they are unusually invested in customer support.

Sometimes there's a straightforward, single workaraound that could be usefully distributed, but often there's not. The exact workaround that a user would need can vary depending on how the user is using the software and what they're trying to accomplish.

Because of that, at least a minimal amount of investigation is necessary to be able to determine what, if any, workaround is available for that particular user's situation.

That means that a conversation with support is necessary.