According to EU (The Old Republic materials, I'll need to hunt down specific cite), the basis for Hutt domination was the fact that

* Their planet was part of Rakatan Infinite Empire

* During the fall of Rakatan empire, Hutts gained access to Rakata technology; which was what ensured their power (as per Wookieepedia, most of that early history is not well known and the main source in EU canon is *The Essential Atlas*).