Cost will be the biggest factor.

SE would need to hire VAs of both sexes for each language that the game is written in, the cost climbs to the many hundreds of thousands of dollars or more.

Bioware put themselves in a corner by doing 100% VA work for SWTOR and because it was expected every expansion and its subscriber count dwindled each year they now make pathetically small expansions every 3+ years because its just too damn expensive . Many of the great British VAs ( performance artists as they like to be referred as) you hear in games come from Theatre / BBC television stock and are part of unions that grant them great salaries inc post release bonuses.