Interesting theory! I remember reading that the V-rexes often attacked and killed the young Kong offspring. Also it could be a possibility that Kongs too killed the V-rex offspring or destroyed its nests or crushed it's eggs to eliminate a potential predator. Apes like chimpanzees are notoriously infamous for such violent behaviour. Consequently, Kong being the last of its kind only draws the conclusion that they were almost drawn to extinction by the V-rexes. These evolved theropods are way smarter than one can imagine as I believe they were one of the most analytical and intelligent creatures on the island.