I think the reason why is as a historian, I've been expecting this for two years now. However, it was not as much of a thumping as I expected.
We could have done a lot of things that would have minimized the damage (better candidates in certain House and Senate races for example) but I already expected to lose the HoR and the Senate would be 1 vote either way.
Yeah, I'm strangely sanguine about the whole thing, too. Not that it doesn't sting, but I guess I've been through enough of these things to know life goes on.