There are plenty of theories of what happened. For example, Harris did target the center and the not-convinced-by-Trump republicans a lot, which is probably what alienated her voter base more than saying something that was already said during Biden election and did not alienate them.
I really doubt you can seriously pretend that the Democrats would have done better without their share of lying. Maybe yes, but maybe no, and concluding one of the two is just as valid as the any other conclusion. One may can even argue that they did not lie enough, as the lies on the Republican side did helped them a lot (unless we consider that republican voters are intrinsically more morally bankrupted than the democrat ones, and that republican voters like lies while democrat voters don't).
As for the fear/hatred, it's a funny thing. If you put one liar and one honest person in the same room, one will say "the other one is the liar" and the other one will say ... "the other one is the liar". It's funny that if you put someone who want to use fear and hatred for their own profit and someone who don't, the first one will say "if you vote for my opponent, it will be very dangerous because their are pushing for fear and hatred" and the second one will say the same.