You think the cost on one extra karma point over the bonding cost will completely destroy the incentive to make your own?
Someone has to make them. Do you want to spend the nuyen to pay someone or the time to do it yourself? (And karma/BP for Enchanting skill, admittedly.) Do you need a custom design rather than whatever shape/design/Force/type they've got on the shelf at the moment?
I'll admit none of these are overpowering reasons, but then what sense does it make for every magician to want to learn enchanting so he can get karma free toys that seriously reduce the incentive to improve skills, Magic, and initiate grade the hard way?
Personally, I'm pissed that Armorer skill won't let me make a rocket launcher out of tin foil in ten minutes for ten nuyen. MacGyver is a perfectly valid character archetype, damnit!!!