SRQ has been removed from Nemesis, Air, Rita, Thirteen, Spinball and Oblivion in addition to the 1 year break on Smiler.
Smiler and Thirteen SRQs were removed when the bag rooms closed, as they needed fastrack to go straight to the station which left no room for SRQ. This was clearly cost cutting to reduce staffing on these rides.
Nemesis lost SRQ as, due to poor implementation, it reduced the overall throughput of the ride by about 3 trains per hour. Clearly this defeats the entire point - a few people benefitted but most were worse off (and unlike fastrack, there's no profit in it either).
Rita SRQ was basically useless as it was almost always at least as long as the main queue, no loss there. These days they need the fastrack queue capacity, SRQ seems highly unlikely to return here.
Air SRQ closed when it became Galactica as, like Smiler/Thirteen, fastrack was directed straight to the station. This was probably due to the reduced capacity which meant a long wait even from the original merge point (I'm guessing here, it's not cost-cutting though as the old merge point was still staffed). They could probably bring SRQ back if they wanted to, though it would require the merge host to at least try to send odd numbered groups to the correct station.
This just leaves Oblivion and Spinball. In both cases, there is no obvious cost saving in removing SRQ. My best guess is that they just made a decision to remove SRQ from the whole park as it coincided with the removal of SRQ from Smiler and Thirteen. Spinball's was repurposed for fastrack, but there's no real reason why the old fastrack queue couldn't be used for SRQ - it's certainly big enough as you'd be waiting ages if it were full. Spinball's SRQ was supposed to be returning but I've not seen any evidence of it ever happening, meanwhile Oblivion's could return right now if they wanted it to.