Ninety five percent of all martial arts training is based on the assumption that the person doing it has normal physical abilities. Unfortunately, since most defensive tactics are based in the martial arts, this idea was carried along in the translation. In other words, when all else fails, we can always use brawn. You can make it work by powering through it. There is an attitude that maybe muscle doesn't work so well, but it is a proven fall back from something that is even more unreliable.
Every officer knows it's going to be a lot of work, but it gets the job done.
And people used to think the world was flat, too. Unfortunately, using muscle to patch a takedown that is not working is one of the main reasons that takedowns fail in the first place. By expecting to have to use muscle to make a it work, we unconsciously position ourselves in ways where we actually LOSE power rather than gain it. By expecting to use muscle during a takedown, most officers not only create a self-fulfilling prophecy, but piss away power that they could be using to control a perp. Many lose more than that.