Harley did make a hardtail motorcycle and the hardtail motorcycle design was standard for motorcycles in the early 20th century.
Hardtail motorcycles had a single, rigid frame and no rear suspension and were popular because they were inexpensive and also easy to produce.
Although the hardtail motorcycle is less comfortable than other motorcycles because you feel every bump in the road.
Harley Davidson eventually introduced their soft tail motorcycle which has a rear suspension system and also shocker absorbers which provide the rider with a smoother ride.
The soft tail motorcycles are more expensive to make than hardtails but they are more comfortable.
Hardtail motorcycle frames and hardtail motorcycles are becoming rare and are often considered vintage and classic.