As mentioned by other comments, water plays a huge role in absorbing and transporting heat as well as diffusing and reflecting light. As a result, many non equitorial regions are just as sunny as equitorial regions.
Your core premise also has a lot more nuance than you seem to realize. We have seasons because the earth’s tilt moves the maximum solar radiance up and down the tropics. The equator is only the sunniest latitude during the equinoxes. The change in latitude of the sunniest spot (subsolar point) shifts the fastest during the equinoxes since that’s the steepest part of the sine wave. The subsolar point stalls over 23.4 degrees N in June and 23.4 degrees S in Dec. These are the Tropic of Cancer and Tropic of Capricorn https://www.wikipedia.org/wiki/Subsolar_point The increased length of day also exaggerates the effect of the subsolar point drifting. That makes the intensity of summer heat worse than the heat the equator experiences. Any latitude between the tropics actually has two periods of maximum solar intensity per year. If you look at a map of desert biomes, a lot of them are near the tropics.
Check out this map of average daily solar irradiance.
https://nsrdb.nrel.gov/assets/NSRDB Graphic Update 2021 09 22.6d4966d2.jpg
As mentioned by other comments, water plays a huge role in absorbing and transporting heat as well as diffusing and reflecting light. As a result, many non equitorial regions are just as sunny as equitorial regions.
Your core premise also has a lot more nuance than you seem to realize. We have seasons because the earth’s tilt moves the maximum solar radiance up and down the tropics. The equator is only the sunniest latitude during the equinoxes. The change in latitude of the sunniest spot (subsolar point) shifts the fastest during the equinoxes since that’s the steepest part of the sine wave. The subsolar point stalls over 23.4 degrees N in June and 23.4 degrees S in Dec. These are the Tropic of Cancer and Tropic of Capricorn https://www.wikipedia.org/wiki/Subsolar_point The increased length of day also exaggerates the effect of the subsolar point drifting. That makes the intensity of summer heat worse than the heat the equator experiences. Any latitude between the tropics actually has two periods of maximum solar intensity per year. If you look at a map of desert biomes, a lot of them are near the tropics.