That's the problem at the moment; with X-Sector and Spinball closed until further notice, Sub-Terra down for an 'upgrade' and other coasters not operating on normal capacity; if a couple of other major rides go down because of standard technical issues there is a big impact on the rest of the park.
I can only assume they are waiting on some parts/hardware for Spinball as it is taking a long time to implement the extra safety levels. With any luck X-Sector will be open within a couple of weeks (minus The Smiler of course). Then it doesn't really matter about Sub-Terra as no-one goes on it anyway!
EDIT:
Just seen that Nemesis started the day on one train yesterday and was only put on to two train operation once a substantal queue had formed. This does concern me as I have never seen Nemesis on one train in the main season, only at FHT. It is becoming apparent that Merlin are very wary of running multiple trains on coasters at present - understandable of course but they have to go on knowing all of their rides are safe.