Not a stupid question. Detroit and Chicago are both baked in pans, if the sauce was on the bottom the cheese would basically steam the sauce. These are pies more like a sweet pie, one big difference though is that with a sweet pie (Lemon Meringue, etc.) you blind bake the crust first to set it, here the cheese protects the bottom. If you ever had an Apple Pie where the crust was a bit gummy, that’s because the crust was not fully baked before the filling was added. (Looking at you aunt Kelly).

Reminds me, I need to try a Hot Water Crust pizza made with the normal sauce—cheese—toppings to see if that works.