Yes but we have no idea when that will happen and Bitcoin crashes less than everything else.
So if we sell in this way and we are wrong Bitcoin will still go up and we'll still make some money. And if we are right we'll save a lot more than if we were holding alts. I'm going to be on the lookout for good BTC/USD liquidity pools to farm which will end up being a great way to hedge against the bear market.

In addition to all this the Bitcoin bear market only lasts and year and alt bear markets can get wrecked in a "crypto winter" that lasts multiple years.