Why is cheese never used in Americanized Chinese food?

It's simple; Americanized Chinese food rarely contains cheese because Chinese food rarely contains cheese.

As many as 90% of Chinese people are, to some degree, lactose intolerant. Dairy is simply not a large part of Chinese food culture. Dairy is growing as a business in China. However, since dairy makes most Chinese sick, I imagine the dairy industry will be primarily an industry of exportation.

EDIT As I promised in comments, I did look for citations for that 90% figure. The figure is ubiquitous. It may in fact have more to do with societal evolution than anything innate in the genetics of the Chinese people, but the fact remains. Most Chinese people react poorly to dairy.

Neato Chart

Jolenealaska is right, that a large majority of Far Eastern people are lactose intolerant.

I think the answer to the question about cheese is that historically the peoples of the Far East did not keep milk-yielding cattle herds, which is why so many of them are lactose-intolerant, and why we never see cheese in Far Eastern dishes.

If someone wants to have a go incorporating dairy in fusion Chinese-Western cooking I would suggest that they go to something like Xueo, a Tibetan yoghurt-like dish made from fermented yak milk. That might match traditional food a little better than cheese!

I think cheese doesn't appear in American style chinese food more because of the way that american style chinese food has evolved (or hasn't evolved) as a cuisine, rather than because milk and cheese aren't traditional chinese ingredients.

I am a Chinese american but also lived in Hong Kong and Taiwan and traveled in China and Singapore, so I'm familiar with americanized Chinese food as well as Chinese food in Hong Kong, Taiwan and China. Food in China, Taiwan and Hong Kong has evolved and changed in really complicated ways as they modernized and got access to new ingredients and exposure to western cultures like Britain and other asian cultures like Japan.

People in China, Hong Kong and Taiwan definitely consume dairy products in spite of whatever lactose intolerance they might have. Milk and yogurt are commonly consumed in China today. Milk appears in certain traditional Chinese desserts (almond tofu jelly and steamed milk). Parmesan and even mozzarella cheese is used as a topping for 'baked rice' in Hong Kong, which are traditional casserole dishes that probably developed with some British influence. Fluffy baked cheese cake is a popular dessert in Hong Kong and Taiwan bakeries (probably result of Japanese bakery influence). Milk is very popular in beverages like milk tea, yin-yeung (mixture of coffee and tea), bubble tea, and coffee.

While food in China, Hong Kong and Taiwan has evolved to incorporate nontraditional ingredients such as milk and cheese gradually, it is curious that this hasn't happened with american style chinese food despite the availability of milk and cheese products.

"Americanized" Chinese is not an invented cuisine, but rather an adaptation by Chinese immigrants to the US to adjust for local palates. That subset of cuisine as a whole still stays largely true to traditional methods and ingredients. While you may see the incorporation of more localized produce, it would be very unlikely to see such a foreign ingredient as cheese introduced. Probably the closest you'll ever see is the cream cheese in Crab Rangoon.

Restaurants are businesses first and foremost. In areas where Hispanics live Chinese restaurants serve cheese and meat enchiladas, pizza, baked fish with cheese topping besides all traditional chinese foods. Maybe this is Mexicanized chinese food.