I suppose for better stuff, but for the average collector they are trying to budget for cons too and there may be less money for ebay. plus they sell stuff to raise $, and all that hitting the market may depress prices. I sell stuff to pay for summer vacations too. funny though, in my neck of the woods it is not Con season. our two biggest shows at October and December, although there is one in the Spring too usually.
But I guess you are right in a sense, a few years ago I was selling a lot here, keys, minor keys, hot books, right around when Guardians of the Galaxy was coming out and all that stuff was hot, and I did a bunch of big group sales to dealers on here stocking up on inventory for upcoming summer shows.