Thing is the only people who care (PRC) have their own satellites, probably more of them than anyone but the US and Russia. And you can bet they've photographed every inch of Taiwan. China's problem, then, is NOT to get images but to identify locations worthy of further attention. It could save them a lot of time to go on google maps and scan for areas with blurring or just suspiciously low resolution.
Note that this is a different situation from not wanting to let non-state actors i.e. terrorists get a look at what's on the roof of the White House. That may be misguided as well, but it's probable that Al-Qaeda has no other way to get that information. Also, it's no secret at this point that there's SOMETHING up there poised to shoot down any incoming plane, so we're not giving anything away by hiding it.