Mining investment continues, we saw a 10% jump in difficulty at the last adjustment. My pet theory is that it is miners who are providing the liquidity despite most of them being long term bullish, not just to pay expenses but also in an attempt to keep the price artificially low to protect their market share by keeping mining less profitable for new entrants due to upfront costs. But with each dump attempt, the liquidity gets soaked up and held. I believe that this market share protectionism is also primary in the blocking of SegWit as well
This doesn't make much sense overall
If we assumed that you were somehow right (that miners are keeping the price artificially low), then it would make sense to keep the price low at any time, not so much to make mining less profitable for new entrants as to crowd out other miners. But the latter seems to be even more unreal since they are there for profits after all, not for losses, and as you yourself say, most of them are long term bullish, anyway
this theory can not be true only because miners can not hold price down forever and it has been a long time since bitcoin was created and even if you consider it after the shaping of mining farms there is still a good couple of years and no one can really hold price down for that long.