I'm pretty sure it's not a license issue.
The military model kits market is much larger than the automotive related one, and Tamiya concentrates on that one.
Also as far as the automotive market is concerned Tamiya prefers to produce RC models rather than static ones.
They produced the 1998 GT1 Porsche in 1/10th scale as a RC kit.
They did the Sauber Mercedes C11 too as RC kit.
The also have the BMW Z4 coupe and many others produced as RC kits but no static kits.
I'd buy any of the above in 1/24 or even 1/12 scale, but they will not bother to produce them.