Find your Jihadi — All the wild chiles are extremely hot; mild chiles have been bred to be larger or milder (or for other conveniences, such as remaining on the plant, rather than dropping when ripe, and hiding under the leaves so birds can’t see them) by human beings. Conceivably habaneros evolved in a very competitive environment, but Capsicum annuum and C. frutescens chiles do just fine in the tropics too. Maybe the colossal spiciness of habanero is just a random variation that became established.
I’m wondering whether chiles are red to attract birds (don’t know whether birds have color vision), or whether plants in the Solanaceae family just tend to have red or orange fruit, e.g. tomato, tomatillo (though consumed when green), tamarillo, wolfberry, ground cherry, some of the wild eggplants.