Touch does one thing from a “contract” perspective:

Ensure the timestamp of is

You can pass -c to not create a file, but it does go against the philosophy that it creates them by default instead of that being an option

EDIT: Looking closer into the code, it would appear to maybe be an efficiency thing based on underlying system calls

Without that check, touch just opens a file for writing, with no other filesystem check, and closes it

With that check, touch first checks if the file exists, and then if so opens the file for writing