I'm not one of those people, but I think that some of them think that just because the price has thus far always recovered, rebounded and spiked higher, it's the safer bet to just hodl than to try to guess which way the market is going to go.  Anyone who's dabbled in trading has at some point guessed wrong and ended up losing out on profits or even outright losing their own money.  It's this fear that drives the hodl mentality, i.e. "it's always recovered and soared before so surely it will again.  All I have to do is ride it out until then."

Then there's the people who tell others to hodl for their own selfish reasons.  They want everyone else to hang on so that there's less sell pressure while they unload their own bags.  These are usually the people who keep parroting the whole "buy the dip" nonsense, even when anyone with an ounce of sense can see that the price is still too high.

With that said, at some point, the bottom will be reached.  If you think that we're still a ways off from that point, then of course it makes sense to sell now and rebuy later like you suggested.  Don't get mad if you guessed wrong and end up losing out.    Just remember, fortune may favour the bold but being bold is often foolish.