Spicy food has a history, particularly in the US, of being associated with masturbation and hypersexuality. Puritans wants food as bland as possible.
In Europe, after the colonial era started, spices became more widely available and were no longer a status symbol (as they were previously only available to the wealthy). This led to the elites turning their noses up to spices and a belief system that the base ingredient should not be defiled in flavor by spice which eventually bled over into the rest of European culture.
Serving richly spiced stews was no longer a status symbol for Europe's wealthiest families — even the middle classes could afford to spice up their grub. "So the elite recoiled from the increasing popularity of spices," Ray says. "They moved on to an aesthetic theory of taste. Rather than infusing food with spice, they said things should taste like themselves. Meat should taste like meat, and anything you add only serves to intensify the existing flavors."
"In Europe, meat was considered the manliest, strongest component of a meal," Laudan notes, and chefs wanted it to shine. So they began cooking meat in meat-based gravies, to intensify its flavor.
Cooking with spices is different from spiciness specifically but I think the same principles apply (with regard to perceptions at the time).