Some states are in early voting right now [0]. That typically means that there's a very limited number of polling stations open. For instance, in Pinellas County, FL there's only 5 early voting locations, compared to 301 poll locations during election day. That's a 60x discrepancy! This is for 713,000 registered voters. Pinellas county early voting also doesn't start until next Monday, October 19.
I think there was likely not much thought put into the number of early voting locations. It's always been viewed as a low-budget, customer-friendly alternative to voting on election day. That probably should have been re-evaluated given the pandemic and the likelihood of greater numbers of early voters.
And by far, the biggest problem is that election day is always on a Tuesday and is not a national holiday. IMO this would be the best change to make first, to enable more people to be available for voting.
[0] The availability and dates of early voting are determined at a state level.