Because Harleys have gobs of low end torque. No need to worry about stalling at takeoff. Torque where you NEED it. From a stop light to maximum posted limit.
And the sound. What a majestic sound the Harley makes! I have gone out to the garage, fired it up and sat in a chair just to listen to it.
For many folks, a Harley in not a good first bike choice. Get something small and light that you can flat foot.