These miners are probably making USD or some other foreign fiat at the end of the day which adds to the supply of foreign reserves without needing to use trade... And if they're siphoning power to get around currency exchange limits moving wealth abroad then a traditional crackdown to confiscate their equipment would be much more effective (you can't exactly "hide" a mining operation).
Frankly China, with so much mining output, benefits more from seeing crypto moon than crash...
(Also "collapsing the price" is something that can be done (and may have actually even already been done in the past) with far far less effort than an attack...
(As one example, articles pointing out that "China can do 51% attacks" are much more effective in crashing crypto prices... maybe keep an eye out for those