UAW has publicly stated they are withholding endorsement of Biden until he supports the UAW’s efforts to unionize electric vehicle facilities. That has yet to happen. Biden has actual influence over the big three that rank and file don't, standing on the picket line is very performative unless it's followed up by action.
For all you libs who take this criticism personally, understand that this is a good start. But that's all it is. Applauding this without critical analysis is how Democrats diffuse political energy without delivering material gains. The working class cannot sit back, the pressure must force their hands to do more.