>the candidates you mentioned only did well in limited/specific geographies
That is because the other candidates all took their own piece of the pie. The republican and democratic primaries were very similar. You had someone framed as a populist outsider who was selling themselves on their ability to fix the system. On the democratic side you had one other establishment candidate who more or less campaigned on the status quo. On the republican side you had numerous establishment candidates that basically campaigned on the status quo who split the vote and several outsider candidates that never had much support at all. The democratic side was consolidated much earlier around their candidate. The republican side never consolidated around an establishment candidate because it was never clear which establishment candidate was the favorite. This allowed Trump to succeed with his consistent 20-30% of republicans in early primaries.
That is because the other candidates all took their own piece of the pie. The republican and democratic primaries were very similar. You had someone framed as a populist outsider who was selling themselves on their ability to fix the system. On the democratic side you had one other establishment candidate who more or less campaigned on the status quo. On the republican side you had numerous establishment candidates that basically campaigned on the status quo who split the vote and several outsider candidates that never had much support at all. The democratic side was consolidated much earlier around their candidate. The republican side never consolidated around an establishment candidate because it was never clear which establishment candidate was the favorite. This allowed Trump to succeed with his consistent 20-30% of republicans in early primaries.