An acquisition of St. George Bank by rival Westpac won’t start the wave of Australian banking mergers and acquisitions some are apparently hoping for.

Westpac is offering to buy St. George in an all-share offer expected to be worth at least A$15 billion. The deal will vault Westpac to the top of the market capitalization rankings for Australia’s banks, and certainly create a strategic headache for Westpac’s large rivals - with the combined entity set to take 25% of the country’s home-loan market.

But there are good reasons for them to resist chasing it with a domestic acquisition of their own. So a run-up in bank share prices Monday - of as much as 7% for expected targets - is premature.

Australia’s four biggest banks are prohibited from buying each other under the country’s Four Pillars policy, which is designed to protect consumers. St. George is fifth largest in the country.

And there’s a lack of compelling targets beyond St. George that will stack up against this deal.

Locally focused banks such as Bendigo & Adelaide Bank or the Bank of Queensland do offer regional diversification. But with market caps of around A$1 billion to A$3 billion, they hardly offer buyers the transformational prospects that St. George will for Westpac. There are some potential targets out there, like the Australian subsidiary of U.K. bank HBOS. But that’s hardly sowing the seeds for a merger boom in the industry.

And challenging Westpac for St. George looks futile. The deal’s main driver looks to be Westpac chief executive Gail Kelly, who was until recently St. George’s head. It’s hard to imagine anyone else convincing St. George’s shareholders they’d be able to merge. –Andrew Peaple