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 WookiepediaWookieepedia, most of that early history is not well known and the main source in EU canon is The Essential Atlas).