Since the amount of Bitcoins introduced into world daily is near constant (except for the scheduled halving of the rewards every few years), SOMEBODY is selling most of the freshly mined coins without disrupting the market.

It doesn't really matter how high the difficulty is or who the miner is the coins are mined and most of them sold.

There might be a small fraction of coins which are still mined in pools using outdated miners and those people don't bother selling them coins(fractions of coins that is).

It has been accepted wisdom that most mining operations sell most/all of their mined coins.