ASIC makers have the biggest risk and cost in investing into BTC than anyone else. And miners have the most incentive to keep BTC fungible and liquid to keep its value.

These guys would have to liquidate a lot of bitcoins smoothly to cover their massive costs and not to deeply disrupt the markets. And they are not interested in playing bad games with people's transactions as this will cause either of two things: the value of BTC may easily go down, and their blocks may be censored by other miners who don't like the value to go down. Every miner thus is motivated to be nice to everyone and maintain his business even if he has 80% of hashrate. Some pools were even addressing concerns of 50% power by limiting their own userbase. No pool wants BTC price to crash only because it got too big and frightens people.