@facw As @jminer pointed out, in MO you get a paper temp tag from the dealership, which they get as a book of blanks from the state. St Louis is also right on the border with IL, so you have a lot of people who buy a car in one state and live in the other. You'd see a lot of temp tags even if you did issue real plates at the dealership for in-state buyers.
All of the things that you bring up require money and technology that are hard to come by in most of the state. For St Louis in particular, there is also widespread hostility toward police (which is beyond reasonable but not entirely unjustified). That makes funding more advanced enforcement tools a tough sell, especially when much more serious crimes are completely out of control right now.