No it's not because of the holiday season.
Well, maybe a little bit but as far as I know, Litecoin recently got a lot of attention along with others like Dogecoin.
Therefore, people have been buying up AMD cards left and right; even the old generation cards like 7950/7970/7990 have seen price increases due to demand.
On the other hand, prices on nvidia cards seems to be pretty stable/same.