8 Reasons WWE's Money In The Bank Concept Is Played Out
2. It's Hard To Book Babyface Winners
Of the three that remained a babyface after their cash-in attempts (Cena, Van Dam, and Punk the first time), their reasons/methods were all noble. Cena and Van Dam, as noted before, gave the champion notice, a save-the-date, for when they would be officially gunning for the belt. In Punk's case, Raw was without a World Championship, and he had to beat a wounded Edge and take his belt for the good of the brand. Punk's ethos of the time wouldn't have jived with taking advantage, but there was a plausible reason why he did.
Tacking onto the previous point, it's not a match designed for babyfaces to win, due to the nature of most cash-ins. WWE prefers the 'shock' cash-in on a wounded champ, and most 'heroes' don't function by that opportune method.