1) Scar was more interested in power than sex. This shows that for all his meticulous planning, Scar could be short sighted on some things. This could serve to enhance that scene in the Broadway production where he realizes that he needed cubs. In the movie verse (where I primarily focus on), Scar was more about control and exercising that right.
2) Scar knew he was unpopular and the lionesses did not like him either. In a sense it was like an open secret that he would not mate with any one of them hence why no cubs were produced. I don't think he would even go as far as 'forcing' himself on one. Maybe he and Zira had a little something something back there


I am on the fence of him forcing himself on any lioness in spite of what happened in the Broadway production which is an AU (female Rafiki, anyone?).