Your first premise is completely wrong, bitcoin is not in a bear market, at the moment it is just moving sideways which means we are in a period of accumulation in preparation for another ATH.

With that out of the way we need to consider the next, the bull run we experimented during 2017 is completely different than the one we are seeing now, back then hype in the altcoin market was incredibly high but now things are different, institutional investors are finally in the market but they are only interested in bitcoin which has marked the huge difference in performance between bitcoin and altcoins, and in the case bitcoin entered a bear market I can assure you most altcoins will drop like flies while bitcoin will still remain quite solid.