Because learning is something that happens through iteration and by combining new ans acquired knowledge together, it is sometimes simpler to learn some of these concepts by simplifying it to the essentials, which is good enough for a majority who will never go beyond that.

For example, the formula for the acceleration of gravity on Earth can be rounded to 9.8m/s². But that would be in an ideal situation, absent of air friction and other variables. But for most purpose and for learning, that is good enough.