Westpac, one assumes, is willing to let market share go for a while.Maybe Westpac has had its fill. Or maybe it does not expect to lose much of its natural share in the mortgage market, which is proving so concentrated and so rewarding for big banks.At October 2009, Westpac held a 23.5 per cent share of the home loan sector, behind the market leader, CBA, with 25.6 per cent.Westpac expanded its home loan book over two years by 40 per cent, looking at the gains made under its own and Rams brands only; and by 34 per cent if the underperforming St George and Bank of South Australia brands are taken into account.This pace is really too much for the bank. Quality and timeliness have proven lacking in Westpac's mortgage business at times this year, a factor notable, unfortunately, for being a common problem across the banking sector. EDS has the contract to service mortgages for Westpac under a nine-year contract, now in its last year, and with minimal chance of renewal.The transition to a new supplier is likely to test Westpac's capabilities over the next year or two. Then there is the parallel project to meld St George into Westpac, a task consuming many middle managers, and one where timetables appear to be slipping.There are thus strong undercurrents pulling Westpac toward higher prices in the mortgage market.Many Westpac managers, though, must be surprised that others passed up the chance for easy, extra profits.