Laws, availability, how long you're willing to wait, and knowing where to look, all play a part in that. For example, everyone and their dog in the US can have real guns, in the UK, hardly anyone can. Yet in the UK and throughout europe it seems pretty easy to get a fully built, yet, demilled Sterling without much issue. In the US, though, it has to be hacked up to little bitty pieces and you have to unweld everything, create a whole new barrel without running afoul of federal law, and then weld all the pieces together again, repaint, etc.
So even here, you get the kit, it takes a while, and ability to get the base gun. Order a 3d print or casting and you've got it in a couple weeks or so. Resin kits are never more expensive. Most pricey are full 3D prints. People will buy hyperfirms or other castings to troop with as it's MUCH easier to troop with a 1lb blaster than a 5lb real one. There are all sorts of reasons...I grabbed an airsoft because i want a good looking all metal E11, but I have no chance at all of making a metal barrel and doing all the unwelding and welding. Just isn't happening.
