The home-purchase market will continue to drive the mortgage market in 2005, industry economists predict, as consumers focus less on refinancing and adjustable-rate mortgages begin to lose favor. Frank Nothaft, chief economist at Freddie Mac, predicts loan volume in 2005 to reach $2.4 trillion, compared to the $2.8 trillion he expects in 2004. Meanwhile, Fannie Mae chief economist David Berson foresees next year’s total origination volume to clock in at a slightly slower pace: $2.15…