Your post about the mining math is right but I hope people don't realize it! About 12-36 hours after rewards drop on typical alts the mining power will drop disproportionately.
[Block reward/(hash price * diff)] is the ultimate indicator of relative mining opportunity for any POW chain.
I think people don't like to mine in the middle due to fear of wasting money on a coin that may not pay out. These days a crypto won't hit an exchange until it is mined out. Its all a crap shoot.