Many many times I have had to plead with various waitstaff for spicy food. Sometimes they will honor my pleas and sometimes they won't. If I order something spicy without pleading, sometimes they will warn me against spicy dishes. The vibe I frequently get is that people have complained about spiciness before to them (one restauranteur told me that was the case).
I want to be sympathetic with someone who doesn't like spicy food. But there has to be some way to accommodate them without turning the entire spicy cuisine infratsructure bland.
I could suggest that people who don't like spicy food avoid cuisines that are known for spiciness. This might be unfair, of course. There are times when you're with a group of people, or maybe you like the non-spicy versions of the various dishes.
If the scenario the restauranteurs are worried about is people being upset about spiciness after the meal is served, how about being pre-emptive? Find out in advance of ordering if a dish is spicy and maybe avoid ordering it, or make a special non-spicy request. Anything to avoid scaring them away from preparing it spicy for those of us who like it that way.
I realize that a lot of non-spicy eaters may do this already, and maybe the waitstaffs aren't responding to offended customers but rather are making stereotypical assumptions about their customers. If so, I don't know what we can do but reward the purveyors of spicy food with our patronage. But if anyone out there has complained to a restaurant about the food being too spicy, think of us before you do so!