No supporters showed up to greet Kamala Harris as she returned to her hometown of Oakland since Inaugration.. but you said she's so popular?

SHE did not get ANY votes. 

I'm not aware of what you're talking about, but the Biden team likely did not have a public event for Kamala Harris arriving in Oakland. Since there was no public event there could be no crowd there to greet her. In addition, California is in the midst of a wave of coronavirus and Californians take the disease more seriously than most conservative people do.

Answers been pointed out before, the use of crowd size as a proxy for overall popularity is incredibly problematic. That's because the subset of people who will attend a political event is much much smaller than the subset of people who will actually vote. Such a metric also does not take into account people who are lukewarm, or even reluctant, supporters of a candidate. The reality is that probably only the people who like a candidate the most will attend a rally and listen to them speak for an hour or two. But the vote of the most lukewarm Joe Biden supporter counts just as much as the vote of the most hyper enthusiastic Trump supporter. The use of crowd size is especially worthless in this cycle because of the coronavirus. The Biden campaign essentially stop having Live Events once the coronavirus Crisis began. This means that any sort of comparison is meaningless. Biden actually cared about his supporters and didn't want to spread the virus so the few in-person events that they had were intentionally limited to just a handful of people. This contrasts with Donald Trump who does not care one iota about his supporters and was willing to see them die in order to hold traditional pre pandemic style events which gave him the attention high that he desperately craved. The number of votes that Biden got was entirely predicted. He was always the more popular candidate than Trump. Furthermore, the distribution of these votes was basically what one would expect. Biden did well in the traditionally Democratic strongholds of the north east and the west, and then pad knauer wins in swing States. Many of these victories, including the ones which were crucial in the Electoral College, came in states where Republicans control the election apparatus thus making the idea that there was pro-democratic fraud particularly ridiculous