Why there was no serious version of 10cc's I'm Not in Love sans Kathy's part

It's too bad that in 1975 British band 10cc might have taken a break from having a wacky sense of humor and started concentrating on a serious relevant version of the bittersweet heartbreaking ballad, "I'm Not In Love", minus Kathy Redfern's self-parody and believe me it is 10 times better than the epic 6-minute version of that song with her part added.