This is definitely a huge factor.

A 2 party system is another one. Some founding fathers even wrote against it [1]

[1] https://ritholtz.com/2011/07/founding-fathers-beware-two-par...

Maine and Nebraska are the two states that don't do winner-take-all. Most states won't switch to proportional allocation because the party with the most political power in a state is likely to lose electoral college votes by switching.

> In forty-eight states and D.C., the winner of the plurality of the statewide vote receives all of that state's electors; in Maine and Nebraska, two electors are assigned in this manner and the remaining electors are allocated based on the plurality of votes in each congressional district.[1]

[1] https://en.wikipedia.org/wiki/United_States_Electoral_Colleg...

True, but that's arguably just as difficult a change to make. Either getting enough State's to swap that the ones that don't are insignificant, or amend the Constitution. If it comes down to state-level changes, the threshold for that popular vote compact may be lower.

In a proportional system there is no reason for a presidential candidate to do anything but rack up numbers in the largest states where they've support. Everywhere else would be ignored.

It's still an issue in that this wouldn't afford equal representation. The way the number of electors is determined is {senators + members of congress + 3}. Since the senate affords massively more representation per person to rural states, rural states will be overrepresented in this system as well.

small price to pay to unlock everyones' vote mattering instead of just a couple battleground states.

Also, giving a bit more representation to less populous areas may be a feature you don't want to get rid of quite so hastily.