They're not loaning it to the Fed, they're borrowing it from the Fed and loaning it to the Treasury. By doing it this way everyone gets to pretend that the Fed isn't the entity buying government debt, and so it's not "monetizing the debt" and therefore -- somehow miraculously -- it isn't outright theft.

Ultimately though it's not as though banks are making the decision to loan to the Treasury at very low rates all by themselves. It was coordinated how the money flows would happen and it would do two things: allow the banks to repair their balance sheets through "free money" loans and also help the government out of a bind where there was nobody to buy their debt that they desperately needed in order to fund expansions of social services during the downturn.

Personally I think that it's pretty immoral to steal from savers to bail out borrowers, but that's because I'm a saver who's been locked out of the housing market by not having gotten in prior to prices going 2x, 3x, 5x or whatever. Ultimately I think the whole thing is going to end very badly, but of course I have no idea how long it'll take. It might take another 2-3 years, it might take another 20-30. No way to know how long the speculative mania will last.