that's really interesting me
No one really knows. Although then again think this way , diglett is super fast digging mole. It takes maybe 50 years of digging for a couple of normal moles to completely cut down a tree by digging under it. The trees you cut are small and its a fictional creature that can cut much faster than a normal mole so it could dig under it to make it collapse pretty quickly. Maybe its nose it sharp,who knows.
It's a video game series about children owning animals with superpowers and leaving home at the age of 10 without any education to go pit them in cockfights. There's not gonna be a ton of logic in things like that. Diglett is a mole pokemon and probably has claws underneath the ground that aren't visible. There are tons of inconsistencies like this in video games, but they aren't meant to make 100% sense.
The same way Garydos uses thunder, and tropius flies.