Apple hire/lure the creator of Premiere from Adobe the king of low cost editing system to Mac to create a competition against Adobe whose, at that time dominating both the PC and Mac platform in editing system. Thus, came Final Cut Pro whose interface was very similar to Premiere but far more stable(Premiere was buggy) and cleaner look.
By the time FCP reached 3, Apple have taken at least 70% of the Mac editing market from Adobe. Premiere who reached 5-6.5 was still buggy(on both system) and losing Mac's market share to FCP decided to release the PremierePro to fix the bugs and isolate Apple by not releasing the future Premiere on Mac from then.
Btw, I use Sony Vegas the most now. It is amazingly simple yet powerful editing system. IMHO, Vegas is better than FCP, Premiere and Avid. :thumbsup: