You're a bit harsh, sosidge. TBG have made their own molds. I have bought a couple of generations of their Porsche 959 Dakar repros after Tamiya's 1980s car and the cars differ from one generation to the next. They refined their mold to make the bodyshell more and more accurate, and having two original Tamiya 959 bodies, I can tell the TBG body is actually functional. By that I mean you're not afraid to sneeze on it.

Tamiya does usually re-release their cars (perhaps just to keep the copyright active) but they didn't re-release the 959 so that's their problem.

All other bodyshells made by TBG are also in this area of lapsed copyright except the R5Turbo, but they launched that before Tamiya re-released theirs (and T only did a very very short run in a hand full of M05RA kits (not released as a spare part on its own)).

My guess is they didn't rip off anyone. They correctly identified a niche market of frustrated nostalgics and took it. Tamiya only needs to push a button and can have them out of business in a blink if they want.