Depends on the ride, but even if a breakdown is down to a sensor reading false information (which would usually be pretty simple reset, that depends on what the process is in the park's opinion); blurting out on the PA "Sorry guys, we've had to temporarily halt operations due to a sensor not reading things correctly" does not to me (having been on the front line of park operations) seem a sensible thing to do 10 years ago, let alone now...
Of course in a situation like a powercut, then fine, because it's pretty obvious to guests that there's little can be done about it (and the parks USED to deal with them quite well)... But given the chance for someone to easily tweet to or about Towers, or any park, about the faulty sensor on Nemesis and suddenly 1000s of people find out that the system isn't working as it should exactly, can you imagine the over the top reaction that would get? It's bad enough when rides break down on lift hills with zero information...