How come more Pokémon didn’t take up multiple squares in order to appear larger?

Looking back, Snorlax was among the only ones that did this. But imagine approaching a larger sprite of Lugia, Ho-oh, or another legendary. Something intimidating that immersed you in a moment of fear and anxiety. It indicated you weren't just going up against another Pokémon to catch.

You were going up against a force of nature.