In our Centro/SouthTexas and Northern Mexico region pinto beans are the staple in all native Mexican-American homes. No exceptions, not ever. It is only restaurants and caterers that pass them over and use black beans in their recipes. 
It's not that we don't think black beans are delicious It's simply that for our cuisine they are philosophically incorrect. By this I mean that they are incoherent, out of context and clash with both the techniques of cooking and the complementary flavors of local products, the terroir.
Pinto beans are natural to the flavor profile of our TexMex regional cuisine, to its history. They meld with the flavors and also enhance the other local ingredients.
I've found three reasons that restaurants and caterers pass over what is the natural ingredient of this region and instead serve the more boldly flavored and colored black bean.
1. The restaurant specializes in food that is not of this region: Southern Mexican, Central American, Carribean or Brazilian food. Yum, I'm getting hungry!
2. The restaurant does not specialize in those cuisines but wants to use an ingredient that seems more soigné. Wants to appear current and hip. They try their best to link it to their dishes.
3. The restaurant is unaware of or does not care about flavor profiles of cuisines, about historical relevance, contextual coherence and just wants to serve new stuff.
I like the following paragraph from the University of North Texas College of Arts and Sciences "The Philosophy of Food Project."
"Food has meaning.... Food expresses its culture and history (pizza, jambalaya, sushi), ceremonial function (Eucharist, horseradish on a Seder plate), and customary consumption (hot dogs rather than beef Wellington at a baseball game, champagne rather than milk for a toast). Gustatory aesthetics directs attention to both the sensual and meaningful qualities of food and drink."
So it's worth considering that pinto beans in this region are philosophically correct.
