Some things just don't active/active nicely on a budget.
Sure, because of inefficient legacy design choices.
I'm not sure I understand your argument here.
Budget is very much an issue when choosing between active/active and active/passive. Nothing to do with "inefficient legacy design".
For example, consider the licensing and hardware costs involved in running something like Oracle Database in active/active mode (in a topology that is supported by Oracle Tech Support).
In my experience, it's no more expensive in terms of hardware/software licensing costs to run active/active, and actually less in terms of opex costs due to issues raised previously in this thread, as well as a host of others.
Note that running active/active doesn't necessarily mean doing something like running a clustered database back-end, utilizing vendor-specific HA solutions. It can be done via a combination of caching, sharding, distributed indexing, et. al. - i.e., via application structuring and logic.