One reason is perhaps to do with what really happens when someone is trying to win a project. Given that winning involves beating others in the fray, all including the winner would end up making commitments which are higher than the capabilities and competencies available with them at that point in time. This initial gap creates risk right at the beginning and if it is not mitigated in time, would amplify to bigger proportions. This mismatch eventually results in projects running behind schedule which in turn becomes a self-feeding vicious cycle with short-cuts being taken to cover up. That then leads to a compounding effect on schedule slippage.