Must have felt that Carrick could not complete 90 mins or was not playing well (don't think he was personally), and wanted someone who could control the game a bit better, Van Gaal has described Herrera as a controlling midfielder in the past. Often used Herrera this season in a #10 role off the bench because he offers more control when we're ahead.
Schneiderlin's pass success rate was 92%, Carrick's 83%, Herrera's 92%, Lingard's 89%. Stats aren't everything but Carrick used to be the man who was around 90% every game, Herrera's extra 9% = more control after we'd gone 1-0 up was perhaps why he was favoured.