Unions have proven to be a effective mechanism in transferring wealth and power from capitalists to workers, which is why the right despises them so intensely. In spite of that, the left fell out of love with unions in the 1960s and 1970s. Why? For two reasons: first, they tended to be reactionary on culture war issues (remember hard hats beating up Vietnam War protesters?); and second, they tend to emphasize the short-term economic interests of their members over long-term concerns and the interests of the country as a whole.
I can’t speak with any authority on the current status of the reactionary culture warriors issue; I suspect that things have gotten somewhat better, given the changing economy and the differing needs of unions today. The current UAW strike, on the other hand, is clear evidence that the concern about overemphasizing short-term financial interests is still valid. Even leaving aside the obvious public need to limit the impacts of climate change, does the UAW really think it is possible to make America an oasis of fossil fuel vehicles when the rest of the world–particularly China–is building electric cars? Does it make sense for Americans to invest in the economy of the 1950s when everyone else has moved on?
Of course not. One can only hope that Biden can lean on everyone just enough to get a deal that will work for the entire country–not just the workers and the bosses. A lengthy strike will be a big fail for everyone except Trump, who really does believe in reactionary economics. Luddites of the world, unite!