My understanding is that the certification process for each individual model is too expensive and too encumbersome. ... There are rumors that the certification process is nothing more than a bunch of kickbacks.
There are two certification processes:
1. Lab tested (drop test), as well as compliance with a feature list
2. Target certified - certification obtained by paperwork only, including all marketing literature for the gun for several years showing is was marketed exclusively for formal target shooting competition only.
I am sufficiently familiar with the process to be able to say with certainty there is no "kickback" required. I recruited legal counsel for a manufacturer to handle this issue and I would definitely have heard if anyone int the state attempted to indulge in such cretinous mendacity. Any rumors to that effect are simply wrong. Also, unlike CA, there is no application of certification fee to the state and the manufacturer does not have to forfeit a sample of the gun to the crown.
The expenses include the lab test (an independent lab must be used; the manufacturer can't set up their own) and the cost of the staff time and/or legal counsel time if the manufacturer chooses to use counsel. The later can be quite reasonable, as I know of several qualified attorneys who will do a job of this scale in return for a sample of he gun being certified.
The biggest obstacle is the AG regulations. Manufacturers realize that they can have their gun accepted as passing the lab test, put it on the market, and find out later that the AG considers it non-compliant (for example, but refusing to accept that the term "effective" applies to the loaded chamber indicator as they did with Glock). Many choose not to play in this arena for what is a tiny percentage of the US market share.