There are some inner city precincts where there are no actual Republican election judges or poll watchers. These are often high crime areas. I have long thought how easy it would be for the two chief judges, both of whom are Democrats though one signed (legitimately) the Republican line, to just vote again and again after the polls closed. That's my theory on why Dem cities so often report hours after the rest of the state. They wait to find out how many additional votes will be needed.
When Philadelphia reported before many Republican leaning areas of Pennsylvania, I had real hope that Trummp would win. Perhaps there were Republican workers/watchers in most Philadelphia precincts. There is no need to report late if you are being watched for cheating.
To some degree we have to blame ourselves. I opted not to work at in inner city precinct, since it meant driving both ways in the dark.