Pf Pancrase couldn't pay him nearly that much for a fight, and K-1 he already does, and its more kick boxing then anything. Sometimes they have the Judo stuff and other MMA factors and matches. But for the most part its Kickboxing.
And guess what, UFC pays more. And by the sounds of it, that really matters.
What is it that is going to be on your mind when you're on your death bed? Will it be the tedious years of 9 to 5, or the memory of some great acheivement. Maybe a moment you stood in glory to the applause of millions.