Unlicensed Transformers and add on kits blew up in 2008 and have been going strong a decade later. You'll find duds and gems but overall there is are high quality niche items pulling from every aspect of the series that can at least compete with high end takara/hasbro if not sometimes exceed their quality at varying scales.
The KO market is seperate from this but it too has seen a shift from shitty low quality trash to improving/modifying/painting up official molds to become the definitive and cheaper versions of official molds. It's rumored hastak have finally decided to move on these ko companies because they were shitting all over the official product from the movie lines. Of course you have duds and shitty releases but generally most releases are solid efforts.
Also there is so much shit coming out of the unofficial scene that it is almost impossible to keep track of it all and its better to keep seperate generals for that reason alone. However, the transfags on both sides can't keep shit flinging to a minimum with the two official manufacturers and adding more to the mix is a disaster. It's more practical to keep them separate for everyone's sanity.