Always two there are, said master Yoda; A master and an apprentice.

Hence the simplicity of the Sith. While the jedi had a university like structure that integrated itself into the galactic senate, the Sith were organised more into an apprenticeship system. Instead there was a tinkerer who had a mastery of the same elements of the force that were known to the Jedi, and a mastery of talents hitherto unknown to the Jedi.

And why were such talents not used or discovered by the Jedi? Well the jedi follow a rule that the force should only be used for knowledge, events and defence, but never for attack.

A sith was never restrained from using the force for the purpose of attack.