The reason why Daisley and Kerslake left (or were fired...depending on who you talk to) was because they were promised that it would be a band...not a solo act.
Being a band would have meant an equal share for all members.
Daisley and Kerslake were veterans who already made names for themselves in the industry and they knew they were getting screwed...but had experience to fall back on.
Randy,on the other hand, knew he was getting screwed...but,more than likely,felt stuck because he didn't have the experience and skins on the wall to leave just yet.
It was pretty well documented that Randy was getting disillusioned and was wanting to leave Ozzy after the next tour. Even though he didn't say it...you would think that he would have felt underpaid.