What is interesting with the odds is that Biden is favored right about the same as Obama v Romey when Obama had about a 1-2 point lead at this point. He is around half of what clinton was when she had a 3-4 point at this point. Biden is polling at around a 7-9 point lead and is around just -200, same as Obama in 2012.
People seem to be banking on a large polling error. What seems off is that even if there is a polling error it's already baked into the sports betting odds, so you aren't getting the pay out like you did if you bet Trump against Clinton. You are basically betting a line that suggests already that Biden is only up around 2 points.