Chances are that ambient are doesn't provide enough cooling. Maybe you can open only window, or all windows on the same side of your home, meaning there's no draft. Maybe you're in an urban environment, with a micro climate even hotter than outside the city. Maybe both. Heat will enter from sunlight and from people inside, and will exit only very slowly.
There's a world of difference between a house in the countryside, with maybe even some trees providing shade, and an apartment in a densely populated area with very low opportunities for thermal control.
There's a world of difference between a house in the countryside, with maybe even some trees providing shade, and an apartment in a densely populated area with very low opportunities for thermal control.