HSTS is a method to force https on websites. If a browser support HSTS, it will automatically redirect to https if and url without (or with http) is used. This setting is enforced in the IIS configuration for the P2G virtual directory by setting the Require SSL setting for the virtual directory.
This setting is not enforced on the root directory of the website since older browsers might not support HSTS. The rootfolder automatically redirects to the https version by alternative method.