National Australia Bank will presumably abandon its bid for the Australian and New Zealand business of Axa Asia Pacific following the decision of the ACCC, announced yesterday morning, to reject the proposed undertakings by the pair intended to overcome an earlier rejection of the proposed takeover five months ago.Neither NAB nor Axa yesterday conceded the bid was dead, with the two companies formally stating that they were considering their positions.There was even conjecture that NAB and Axa might attempt to press on with the planned merger - convening special meetings of shareholders to vote on the scheme and goading the Australian Competition and Consumer Commission to take court action to block the scheme - though this seems far-fetched given the proposal ultimately requires the approval of the Treasurer, who is unlikely to take a different view to the ACCC.NAB and Axa could also take action in court themselves to reverse the ACCC rejection, and it's the merit in this option that is presumably engaging the interest of the companies' management and board.The trouble with pressing on with an Axa bid is that the proposed takeover always had tenuous merit. NAB, really, is better off without Axa.Investors, an unreliable guide, seemed to agree yesterday, with shares in NAB up four per cent yesterday (partly because the threat of a dilutive capital raising was off the table) and shares in Axa down seven per cent (as short-term investors, many said to be hedge funds, began to abandon their holdings).NAB's bid for Axa failed because the ACCC concluded that the undertakings by the bank and Axa, offered a month ago, would not remedy the loss of competition in critical markets dominated by the pair.This might frustrate NAB and its few supporters, and taking into account that NAB (and Axa) presumably thought that, after months of talks with the ACCC on their options, the undertakings addressed the concerns raised in April.As it stands the ACCC wrote in their competition assessment on NAB's bid, published yesterday, that the undertakings failed to include any distribution network, did not include the sale by Axa of the North investment products (along with the North platform that Axa was to sell to IOOF) and were also "uncertain and dependent on third parties".The ACCC's competition assessment provided more clarity on the underlying reasons for knocking back NAB, and which centre on the removal of incentives for others to invest in investment platforms as the number of owners of investment platforms declines and the incentive for those remaining owners to collude on prices increases.This in turn draws on the ACCC's analysis of the centrality of investment platforms - now dominated by NAB, Axa, Westpac and Macquarie - to retail investment flows and given the convenience of those platforms to financial planners.The ACCC pointed out that NAB would have controlled between 29 per cent and 37 per cent of funds under management and managed through investment platforms, and controlled annual inflows of between 17 per cent and 21 per cent.There are critics