Sakuraba has taken some brutal beatings against bigger men and came back to win, where as Chael has simply tapped at the first sign of trouble against smaller guys.
Chael has 'taken fights' against bigger guys and short notice match ups, but he will only do so when it's a Win-Win situation for him. ie If he loses a last minute fight, he can claim it was because he was under prepared. If he fights a bigger guy, he can claim he only lost because he was at a disadvantage. No matter the outcome of these kind of fights, he gets qudos.
This is why Chael has never been and never will be UFC champ. He has the mindset of a glorious loser, as opposed to a winner. He can't handle the pressure of being expected to win a fight, and he will choke under those circumstances. It's much easier when people expect you to lose. That's why guys like Anderson, GSP, Matt Hughes etc are much ballsier than Chael. They go out every day with the whole world gunning for them and trying to take their titles. That must be incredibly tough. Tapping to bigger guys ad nauseum for a big pay cheque? I'll do that any day of the week.