What is to keep SBD from doing this again?

The simplest reason is demonstrated willingness of stakeholders to support @sbdpotato or something like it. This did not exist in the past and can be done more proactively in the future, rather than waiting until the imbalance becomes severe.

There are some other system changes which make the future unlike the past including the different print rate logic which makes large pumps less likely and some SBD printing shifted from rewards to the DAO, which both changes the print rate logic and also gives greater direct control over the amount of SBD entering circulation.

No guarantees can be made, this is still all experimental, but assuming the same outcomes because an earlier iteration of the experiment using different methods did not work out is not justified.