What they do with the rest depends on the business model.
If their model is to expand then they sell more BTC to get more miners & larger facilities.
If their model is diversification, then they sell more BTC to buy other coins.
If their model is to hold and grow then they sit on the coins.
Yes, Bitcoin miners should regularly sell their new BTC coins for fiat money in order to pay for electricity consumed and cover all other costs. Depending on the situation in the cryptocurrency market, most of the mining pools make a decent profit, so administrators can temporarily hold some of the mined coins. This would be a smart decision on their part because the Bitcoin price is likely to significantly rise over the next 3 years.
I guess the OP calls miners bears because he thinks they always dump all their BTC coins with no remainder on cryptocurrency exchanges. Of course not. Some miners act as long-term investors.