Mainly for three reasons.

1- people are greedy and they think the can make profit by mining without actually understanding shit about mining.
2- most of the hashrate comes from the U.S large firms who use investors money and have little to no risk.
3- large firms in the U.S have some tax "games" they can play to benifit from equipment purchase vs buying BTC.

So just because hashrate is going up, it doesn't mean people are doing the "right" thing.