>>33377185The thing is, WHY didn't Piplup evolve? It may have been for the fact that it was popular and marketable, one of the most iconic Sinnoh Pokemon in fact. It's still pushed to this day. Or maybe, it didn't evolve because, quite frankly, Piplup fits Dawn better than Empoleon does.
With Popplio, the situation is not as simple. If we consider the target audience (japan kids who buy the merchandise), Primarina seems a better candidate, as it has been doing well in that regard, and better than Popplio. Many would argue that a fully evolved Pokemon would not fit Lana's character, though. So I can see it going both ways, but I really don't think patterns are the answer here.
