I hate to tell you this but the average snowboard consumer rides less than 15 days a year so the boots are designed to last about 30 days. That way, the average guy thinks that he got his moneys worth, but the manufacturers and retailers get to make more money by selling you a new pair of boots.
If you want them to last, consider getting a pair that is meant for a "serious" rider. That means getting a stiffer boot that actually has some good support. Boots like the F22,F24, Malamute, Synapse, Ion, Driver, etc. are a better bet for you.
Also, the worst thing you can do in a pair of snowboard boots is to walk around in them all day. All of you lifties out there should buy some Sorels and keep your snowboard boots in good shape.