Trees

Can somebody please explain to me why it would cost between forty and fifty dollars for me to go to a farm and cut down my own Christmas/Yule tree, when I can go to Loews or Home Depot and get a perfectly nice pre-cut tree for twenty or thirty dollars (less if it's on sale)?

Is it because of insurance or something? You'd figure it would cost less, since they don't have to pay somebody to do the work.

Basically, why are they asking me to pay extra to do a job they'd normally be paying somebody else to do?