They don’t matter because most states use winner take all for their EC votes. Every additional vote past 50% is absolutely worthless, as is any vote cast in a state where there’s no chance to hit 50%.
With a popular vote system, every vote would still be worth something. It would be worth a politician’s while to campaign in California because even if they’d normally get 60%, as it’s still worth it to drive higher turnout or try to increase that to 65%. It’d be worth going to a hostile state because a vote is a vote. It doesn’t matter where it comes from; they’d all have equal worth.