The mortgage credit box contracted quickly as the housing market slid toward disaster in 2007, but it’s proving to be much more difficult to stretch it back to what used to be considered normal. The subtitle to this week’s annual convention of the Mortgage Bankers Association could well have been “access to credit,” an idea that clearly dominated the conversation. Despite the recent unexpected drop in mortgage interest rates, most observers expect origination volume in 2015 to track closely to this year’s sluggish level and part of the problem is relatively weak home-purchase lending. Industry people are...