Not trying to scare people, but I believe knowledge is power. Cords can get tied in knots. It is called a cord accident. They usually do it very early, and then as they grow, it can cut off blood supply. My friend lost her son at 38 weeks due to this. This is why the ask you to monitor activity. Her son stopped moving in the evening. When she called the next morning, it was too late.
If you aren't feeling movement, drink a soda, and lie down. If that doesn't work in an hour, call. Better to feel dumb than not have your baby.
First off, it's called a true knot. It's a knot in the cord when the baby swims through a loop early in pregnancy. It's dangerous during delivery because as the cord stretches, the knot pulls and cuts off oxygen to the baby.
Secondly, for SOME people knowledge is power. For others, it freaks them the eff out. OP was already worried enough. She didn't need more uncontrollable issues being thrown at her.
And thirdly, a true knot isn't the ONLY reason they ask you to monitor movement. There are many other random things that can happen, sadly, as PPs have mentioned.