I think a large reason for optimism for (Pres-Elect) Biden in PA is that the outstanding count is mail in. PA early vote is almost prohibitively pro-Dem, and there are plenty of outstanding votes in solid Blue areas around Philly and the suburbs.
In addition, the "red-leaning" Counties almost uniformly reported their election day vote first, and even they have outstanding mail votes. That's even a huge plus for Biden, given that Dems were the main participants in mail voting, even in "red" areas...
We don't know for sure the (pro-Biden) trend regarding mail votes will continue, but the trend is very strong. I heard that in EVERY single state (except the Dakotas) Biden WON the mail vote and conversely (aside from CA, NY, and IL) Trump won the election day vote. So if Biden ends up winning (as I believe he has) he actually won the election in the early vote...
So bravo to Mich Sec of State Benson. She just explicitly pointed out that it was the GOP LEGISLATURE that would not allow them to process mail votes the day before election day (like they do in Ohio) so that they would be able to complete their count on ELECTION DAY LIKE Ohio. Ohio has about 2 MILLION more people than Michigan, so obviously had the GOP LEGISLATURE allowed the ballots to be processed, then Trump likely would not have even had his (mirage) "lead" at 4 am when he made his reckless attack on Democracy...
Coincidentally, this is the exact same scenario in PA as well. Dem Governors and Sec of States (elected by a statewide vote) attempted to apply common sense and streamline the process by allowing the counties to open and process the mail votes prior to election day. (Like they do in states like FL, OH, etc)...
But in both MI and PA, GOP Legislators (elected by a small percentage of the state) thwarted attempts by people elected by the ENTIRE STATE to make this process more timely and efficient. And then with unprecedented hypocrisy, these same Republicans (at least Trump) complain about the vote-counting taking "too long", which is the situation THEY themselves have CAUSED.