I'll say this, in regards to all-around worldwide popularity, I can see King K. Rool being a part of that. The requests were MASSIVE for an entire region alone for Ridley, so I can see that making sense too, for the poll.
However, Simon and Richter? Simon probably have been requested off and on in the past, and Richter probably was added in as a bonus, but to say that he's on the level of Ridley and King K. Rool makes me do a double take. Note, I'm looking at the Smash Ballot as how varying regions would vouch for which characters. (Example: Ridley = America, Bayonetta = Europe, Rex & Pyra = Japan, so forth)
Even adding on how simply dormant the Castlevania IP had been during that time of the Smash Ballot and with what numerous fan-made polls we've seen, I'm curious how Sakurai came to the conclusion to add in Simon and Richter in that deal.
But then again, Bayonetta won the Smash Ballot back during Smash For, so what do I know?