I believe it comes down to Maul wanting to take over Death Watch legitimatically, and therefore following the traditions of the people so that they won't see him as a usurper, but a rightful leader. In Tales of the Jedi, Ulic Qel-Droma fought Mandalore on Mandalore's terms, and won his loyalty by defeating him. Similarily, not all Mandalorians were happy about an outsider taking over the clans during the Sith War. Since Mandalorians admire physical prowess and tactics, they (probably) see the use of the force as a power the weak can fall back on when they aren't fit enough to fight with their body and mind alone. And being Mandalore means being physically superiour. If Maul had usen the force extensively like he would against a Jedi, I doubt many of the Death Watch would have accepted him as their leader. Bo-Katan would probably have been nominated as Mandalore instead. What good is a Mandalore if he doesn't respect his people's traditions?