It could be that, despite many (most?) pizzas having more white cheese, the white cheese is more prevalent but, particularly in the US, cheese is often associated with yellow/orangish tones so they included it to match that expectation. They’re a big company and these came out in the '90s IIRC, so I imagine it was researched and focus-grouped to death before launch and, since two cheeses are almost certainly more expensive than one, there’s probably a reason there are two.
It could be that, despite many (most?) pizzas having more white cheese, the white cheese is more prevalent but, particularly in the US, cheese is often associated with yellow/orangish tones so they included it to match that expectation. They’re a big company and these came out in the '90s IIRC, so I imagine it was researched and focus-grouped to death before launch and, since two cheeses are almost certainly more expensive than one, there’s probably a reason there are two.