Why do hurricane forecasts and reports only show the extent of sustained winds for 34, 50, and 64 knots?

Hi! I'm trying to understand hurricane forecasts and reports issued by the US National Hurricane Center. I get that each one of those values represents a threshold for a type of storm, tropical storm force winds (34 knots), storm force winds (50 knots), and hurricane force winds (64 knots), as [this page](https://www.nhc.noaa.gov/help/tcm.shtml?WINDWAVERADII#EYESIZE) explains. However, I don't understand why it is not provided as a continuum and why it stops at 64 when other information in the forecast indicates that wind speeds will be a lot higher. Thank you for any help!