Normally I would 100% agree with you, it is ridiculous. Guild Wars 2 got an enormous update today, tons of fixes, new features, and new content with zero server downtime. But the existing SF5 servers are so terrible and have so many basic fundamental issues that it's possible they really do need a lot of work on the back end, and that could necessitate a lengthy maintenance period.
This excuse only works if the servers come up and things are a lot better, which probably won't be the case. But it is possible!