If you skate the shoes that are really popular like Era's, Authentics, Chukka Lo's, that's probably the reason why they wear out quick.
The quality has more than likely gone down in the past few years because of their popularity.
I got a pair of Authentics over a year ago, and the sole started to peel away from the upper in the 1st few days. Just from walking around in them. They glue is cheap, so I would imagine they started going cheap with other stuff, too.