Because there is no magic button to push that fixes everything. There are man hours being put in to make adjustments, Investigations to make, data to pour through, tests to be done. A service interruption will only put fuel on the fire, especially if the service interruption results in even poorer performance due to an oversight. It's in no ones best interest to half ass the work.
Since there are multiple discussions ongoing about crashes while in combat, we will be closing this thread. We are currently investigating this issue which is affecting both PC-EU and PC-NA servers. You can continue the discussion in the thread linked below.