Originally posted by xJLxKingNo, the whole point of the arc was that Thanos was needed to do so. Thanos' experiences and his willpower were the reason he was selected. He wasn't just picked out of a hat. To be selected by the supreme being to fix all of reality because you're the best man for the job is one of the best feats out there.
Because TOAA could have done anything to stimulate the situation. Because after all, he could have done it himself if he wanted to.