Why do u think rates are usually written as unit rates

It simplifies it down to how many this happens in that if you know what i mean. like miles per hour. if a car drove 300 miles in 5 hours thats the rate. 300 to 5 ... to simplify, divide 300 by 5. so youd know you were going 60 mph, and thats why unit rates are imprortant. do not copy this answer, change the words around a little bit

Simply because rates become easier to visualize when simplified.