Objectively it's because the Chinese outbreak is well controlled at this point without lockdown measures. Alameda isn't there yet, though the Bay Area is closer than many areas in the US which are still growing.
The public health officials who, believe it or not know more about this than Elon Musk,said they want specific metrics met before opening. Period.
So Elon did what he does and is bullying them. He called the public health official in charge, a pediatrician at Oakland's Childrens Hospital "ignorant" and "unelected". His horrible fanbase is loving it,and spamming the Alameda County offices with complaints. Why doesn't he say that about the officials in China? He'd be out on his ass, that's why.
Because it shows that in a country with a bad outbreak a factory of similar makeup can be operated without exacerbating an outbreak. They reopened the factory in China well before cases were zero in China.