First, there's always the possibility people lie on these polls. This is especially true today. Look at lefty Twitter. If Antifa/BLM
kills an old man, nobody gives a shit; however, if you fucking dare try to defend yourself, you are
arrested and pilloried as a monster. All it takes is one Leftist pollster who hears "Yeah, I'm voting Trump" to leak your number onto Twitter and have a mob come for you.
Second, they seriously massage the numbers no matter what. Anyone who takes a statistics class can tell you how misleading any poll can be, but this is something of a psychological tactic. The goal is to make Republicans feel increasingly isolated and, well, obsolete.
Third, with the pandemic on, this offers the Democrats a chance to push voting by mail and "ballot harvesting" (i.e., send a volunteer to a place full of people who cannot vote in person and collect their votes. Yes, I think it sounds Orwellian too.) Both of these methods have given the Democrats an iron grip on California and reduced the Republican presence to a regional party at best.
Fourth, it's a matter of ego for the leadership. Remember
this little gem from 2016? They improve the polling results to make themselves feel better, the little people's opinions be damned.
Fifth, if Bob is any indication, the rank-and-file live in some sort of Dionysian fairyland where facts don't matter. In their minds, people aren't being turned off by the black bloc tactics of Antifa and BLM, they've got those deplorable obsoletes on the run!
That's my two cents, anyway.