They failed to drop free. But that was fifteen to twenty years ago. First generation Glock magazines were made of all plastic.
The first “NFML” (Non-Full Metal Lined) magazines were designed to do that.
Those crazy Europeans, with their history of magazine heel-releases, wanted to strip a mag from the grip.
The last two or three generations drop right out, no problem.
unless glock was selling them trade in mags dirt cheap to underbid some other company.