Personality is in the eyes of the beholder - and shaped by editors. Judges often make silly comments that some voters actually believe. Regional votes tend to go for people who sound and act the same. People who like bad panto, tend to think people who are bad panto acts, have personality. Brash people like brash people, and can't understand quiet ones. Attractive males are deemed to have personality, while their female equivalents are often deemed suspect. People see whats not there, or in their imagination, ,and miss what is there. Drive and ambition to win are praised in some, and criticised in others. Subtlety is often missed. Lots of VTs, on a credible positive back story, means votes- a few Vts of training problems, becomes a reason not to vote. There's often zero relationship beween who has a successful career, based on personality, outside, and who gets votes for having one on the show. Some of the most popular people around failed to get a vote. There's also the Big Brother problem - that the people everyone involved likes, or function well. are often not the ones the voters vote for.
Anyone, to do well, has to be able to act, and to have musicality. There's also a question of whether the public should vote for people who play a role as themselves, or keep their vote for those who can play the roles required better. The history of the show is full though of cases of bad actors doing well, and good actors proving too subtle - or Len getting it wrong and missing whats there.