It's super unprofitable to mine BCH right now, at current exchange rates (assuming you could even sell BCH, which you can't). Miners stopped to wait for it to become profitable again, due to BCH's special difficulty adjustment. Details: https://medium.com/@jimmysong/bitcoin-cash-difficulty-adjust...
Okay that sounds more reasonable. My original thought was that it's not very decentralized if all the miners can agree to stop mining at any point. Economic reasons seem much more reasonable.
It's not very decentralized. According to https://cash.coin.dance/blocks ten of the 16 blocks so far on this fork have been mined by "Genesis Block 269-273 Hennessy Road Wan Chai Hong Kong", 3 have been mined by ViaBTC, and only 3 by someone else. These two pools together have around 80% of the hash rate on this fork.