Chilli heat moved from a regional preference to a routine menu feature across the United States over the last two decades. The spread has as much to do with how menus compete as with how tastes changed.
Heat is the cheapest differentiator a kitchen has
Making a dish meaningfully better usually requires better ingredients, more labour or more skill, all of which cost money on every plate sold.
Making a dish hotter costs almost nothing. Chilli in dried, fermented or extract form is inexpensive, stores well and can be added at the end without changing any procedure.
That gives an operator a way to launch something that feels new and specific without renegotiating supply or retraining a line.
It converts a dish into a scale customers can discuss
Most attributes of food resist comparison. Heat is one of the few that people readily rank, describe and challenge each other over.
A numbered ladder of spice levels turns a single item into a series of visits, since finishing one level implies attempting the next.
It also generates conversation and video, because the reaction is visible and immediate in a way that appreciating a sauce is not.
The physiology encourages repeat orders
Capsaicin binds to the same receptors that detect heat, which is why chilli produces a burning sensation without any tissue being burned.
Regular exposure reduces the intensity of the response, so people who eat chilli often need more of it to reach the same effect.
A customer base that gradually escalates is unusually valuable, and menus that offer somewhere to escalate to keep those customers rather than losing them elsewhere.
Supply moved before the menus did
Immigration, expanded produce imports and the growth of specialist manufacturers made a wide range of chillies and chilli products routinely available to distributors.
Once a kitchen could order a specific pepper paste from the same supplier as everything else, using it stopped being a specialist decision.
Grocery shelves followed, and home familiarity with those products then lowered the risk of putting them on a mainstream menu.
The limits are showing up in the same places
Very high heat narrows the audience sharply and can overwhelm the rest of a dish, leaving little for a customer to return for beyond the sensation.
Kitchens have responded by separating heat from the base preparation, serving it alongside so one dish can satisfy several tolerances.
The more durable shift is not the arms race but the ordinary expectation that a menu will offer some heat somewhere, which was not true a generation ago.