Yeah, you make a good point. Definitely something I've thought about. When I started working on Diceright, DnD Beyond hadn't even been acquired by Wizards yet, so a lot has changed in relatively short time. That being said, they recently released an alpha of their 2d tabletop and there really wasn't much there. I assume it will get a lot better though.
Still, it was a tough call on what to focus on as DnD really is a huge player in roleplaying games. A smaller slice of DnD users still might be larger than a bigger slice of another game.
In the end, DnD is the game I know the most and the one I love. So I decided to do what I thought would be the most fun.