Before WW2 only the German Mauser, Oberndorf factory offered commercial Mauser actions to the trade. All those original Mauser actions had straight bolt handles. So all the “classic” Mauser sporters by Mauser, Rigby, Holland & Holland and you name them came with straight handles.
FN, Belgium, did not make any commercial Mauser actions until several years after the end of the war. When FN started to offer commercial actions in the 1950s, swept back bolthandles like those on the Winchester 70 were in fashion. As most of the FN exports catered to the US market, FN made swept handles standard on their new commercial actions.
Meanwhile fashions changed again, away from the “California style” of rifle design. Most top gunmakers like the Dorleacs , H&H, Rigby, Westley Richards went back to the classic prewar Mauser style with straight bolthandles.This swingback of fashion came years after FN ceased making "Mauser" actions.