Your caliper is "STICKING", not seized.
I say "sticky" because the e-brake is not retracting, which means it is applying braking force ALL the time. That mimics a seized caliper. I am on the 7th Gen forums, and as our cars get older, our younger peeps buy them 3rd, or 4th hand, some brakes were not serviced properly and when people say gas mileage has gone bad- number ONE is a seized/sticky caliper.
Before your caliper becomes seized, you will have to have the brakes fixed.
The slider pins not being lubed would NOT cause the issue with your e-brake. However, one of the reasons why brake slider pins lose their effectiveness is road salt, heat, and time. Guess what, these evil forces also cause e-brake mechanisms to freeze up. I am perplexed because you say you use your e-brake all the time. Usually the frozen, or "sticky" e-brake happens because it is used once every two years....
So your slider pins are probably greased enough- it is probably just an e-brake problem.
The e-brake is sticking because of something you hit (the beaver you hit is having his vengeance) or because of rust. The bracket could have gotten knocked loose by something you ran over, a valet may have beaten the hell out of your ride (applying e-brake at 30 mph like our man Dom in the Fast and Furious movies), or your brakes wore down, you yanked on the cable too hard after driving through puddles and road salt, and it did not retract in time as you floored it. Who knows?
In conclusion, it is NOT a seized caliper- it is a sticky caliper caused by a dysfunctional e-brake cable.