Sebastian Meyner
Because no model manufacturer invest a huge amount of cash into a new mold, without some market research. The "A" was purchased by a great number of countries (more potential paint schemes=potentially way more interest in the kit amongst modelers worldwide), the "C" is only used by the u.s.. Do the math....

John Wiersma
But the Tomcat is only (except of IranAF) used by the Navy, explain then why there are so many kits off that model...

Treehugger
Is the C model the only one that can land vertically like the old Harrier?

Dietmar Bogatzki
No thats the B model

David Taylor
Different wings and a hook on the C so it would'nt be hard to add a different sprue

oxcart77
The landing gear is also different.

LordH
Japan, Tamiya's home market, bought the Model A and not a Model C.

Maciej Bellos
Tamiya didn't release a long nose Phantom, despite Japan producing the F-4EJ locally. They released the B version even though there are already B models on the market.

I expect somebody (ie Meng) will release a C model as soon as there are quite a few NAVY squadrons operating the type. Obviously an A model will find its way on my bench somewhere around the end of the decade, when the first ones arrive in Greece.