>>13741110Because their designs may be seen as "final", in a way. See, if a Pokemon evolves, they have to change their concept or add something, and this could potentially ruin them. If you notice, most final evolutions add a huge change.. it's very intentional.
Charmander is somewhat similar to Charmeleon, but he grows the most with Charizard where its far bigger and has wings.
Mega's can essentially keep the same design, while adding another mask that's only slightly altered, all-in-all keeping the same relative design core in tact. Mega Lucario is the best example of this.
