There is a federally defined process by which firearms go from manufacturer to retailer to end user. A manufacturer cannot tell a retailer how or to whom a firearm can be sold, that’s done by the Federal Government. The fault for any illegal firearms transfer is with whoever last transferred the damn thing. So when Glock manufacturers a new pistol it’s then transferred (with lots of paperwork) to the retailer. The retailer then transfers (sells) again with paperwork, that Glock to the purchaser. If that end user then transfers (sells) that Glock to another end user neither the manufacturer nor the original retailer know anything about it or have any say in the transfer process.
So on what rational basis is a manufacturer responsible for the downstream actions of others, actions that they cannot control?