It's worth adding that those states aren't even close to as homogeneous as most tend to assume. Only 60% of California voted Democrat in 2016, and you have to assume the turnout for Republicans would be higher if it wasn't guaranteed that their vote (for president) was meaningless. With the current system, you can cater only to the populous parts of California and win the whole state, and that goes for most other states as well. With a popular vote, that ~30 to 40% of California is relevant again, along with significant chunks of other states.

It's also worth noting the math really doesn't work out, the electoral college makes it easier to win the whole thing while carrying less states/votes (Which really shouldn't be surprising). With both the popular vote and the electoral college, you only have to take the 10 most populous states to win the whole thing. But the difference is that, with the current electoral college you generally only need to get 51% of the vote to win the whole state, which is significantly easier and turns states like California from a 60% to a 100%. With the popular vote, to actually win in that fashion you would have to take almost every vote in those states, which is practically impossible considering the diversity.