If cheap acoustic guitars sound bad because the tops are thick, then wouldn't drilling a lot of very tiny holes in the top improve the tone and volume at all? I mean VERY TINY holes...
No. The problem with a top too thick is that it is too stiff and too heavy to properly vibrate, especially at lower frequencies that have higher amplitude. So the sound will be small and tinny. Drilling holes in the top would solve the weight issue, but it will not make the top more flexible.
But the top has an important function: The top is a membrane that is supposed to transfer the vibrations into the air. Creating lots of small holes in the top will reduce the amount of surface you have, reducing the ability to move air. Also the big total opening will reduce the effect of the resonance chamber.
Also cheap acoustical guitar tops might be made from less than optimal wood, which affects vibrations, or occasionally even plywood (this is common in cheap curved tops, as you do not need to carve, but you can simply glue plywood into a matrix under heat and pressure. But plywood strongly inhibits vibrations).