Most chains, especially if there large ones, and fast food in particular have business models designed to appeal to the greatest number. Often this is with a relatively small menu.

Tastes will vary greatly by area and person so “spicy” means spicy by the standards of the least spice inclined of the target demo.

The other thing to keep in mind is are they cooking it, or just heating it up? Restaurants where they cook you food rather than just heating up a prepackaged item will have more control over seasoning/flavor.