I'm a contract vendor these days, and the high tech agencies are competitive and have to offer benefits and perks, training, etc to keep the better talent.
In at 'at will' work state, if you are only working retail or a service job for minimum wage (or close to it) then you will almost definitely be kept below 40 hrs or 32 hrs so they dont have to give you full benefits anyway. And there's no security either. People come and go constantly.
I think temp agencies are a good way to get your foot in the door and make the most of an opportunity.