There were a lot of changes to the Catholic rituals in the sixties under a series of reforms Catholics refer to as Vatican II. One of several physical changes was the removal of communion rails. One effect of this is that there is nothing to rest against if you are kneeling, making the act quite a bit more physically demanding. So standing is both easier and quite a lot quicker than having each person kneel in turn. Before Vatican II and in Church of England (as similar) the use of rails with the minister moving along the entire width makes both ways of receiving almost equally practical.