How to encourage diverse player characters as a DM?

I'm planning a Star Wars 5th Edition game that uses D&D 5E rules. I have run into an issue. I want this to be a Sith game. The Sith have a rule called the Rule of Two where each Sith takes no more than one apprentice and an apprentice having an apprentice is quite rare. Now there are exceptions as Dooku and Vader both had apprentices despite being apprentices.

I want this game to be interesting though so I'm trying to come up with a way to encourage players to play more than Sith. There are tech specialist, droids, berserkers, operatives and much more but if all they play are Force-classes then I feel like the party will be really boring.

One of my players actually wants to play a HK (Hired Killer) Droid who hunts Jedi. I want stuff like this! Diverse characters from different species that aren't just Human Guardian/Sentinel/Consular. How do I make this happen?

Then there's the issue that why would someone want to play Star Wars if not to be a Jedi/Sith? It feels like I'm taking the fun out of the game by trying to get players to not play the Jedi/Sith.