system
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human
ELI5: Why are picture frames so expensive?

So I recently decided I wanted a poster and because I'm an adult, and didn't want my $15 masterpiece held up by tacks I figured I'd get a frame for it. My first stop was a local frame shop where I explained I wanted something inexpensive for a poster. They told me they had a cheap poster package. Simple black stained wood and a basic pane of glass (uv protection, but not anti-glare). Just what I was hoping for, but the total was $80. So I hit amazon and found a basic wooden frame, a sheet of plastic with a cardboard back and they still wanted around $35 (and required you to screw in the mountings yourself). In the end I did exactly what I wanted to avoid and tried walmart where I found exactly what I needed for $16.00. I'd have been willing to pay more for a better frame (something wood would have been nice) but the prices are way out of line when you're just trying to hang a simple poster. What is going on with the pricing on this stuff? Are their intricacies to picture frames I'm missing that make them cost so much more than the sum of their parts? 

EDIT: It's so cool to hear from folks with experience in the framing business. I'll leave this post unsolved for the weekend in case anyone else shows up to chime in and then mark this one explained. Thanks guys! I feel bad for the folks who really do have something they want to protect because it seems like everyone gets gouged, but it's a necessary evil if you want your stuff to stay nice and look great on your wall.
gpt
Those cheap frames are far far far from archival. If you don't have uv glass, the art is going to fade quickly. If you don't have non-acidic backing, it's going to discolor and hurt your image. Then there are things like museum glass that eliminate glare almost completely. You don't realize how nice that is until you see horrible glare on your poster from your lamp.