I don't think this statement is fair. There has been unionization effort across the country throughout the years.
The difference is that corporate media is often very comfortable boosting ideas such as racial justice, but not class consciousness.
Left strategy appears to be terrible is imo because neither party is left wing. There is simply no place in the current political landscape for a labor party/wing to address the issue for the big fraction of the population you mentioned. The republicans pretends to address it, the (majority) democrats dance around it.
Not very successfully. Only 6.9% of private-sector US workers have a union. That peaked at 35% in 1954.
[1] https://www.epi.org/publication/union-membership-data/#full-...
A pithy but I really feel important example: a party with no room for Joe Rogan in it is definitionally not a party of the working class.