The thing is, Din didn’t realize the weapon’s specific importance. So his new-ish ally Bo-Katan Kryze—the sister of Clone Wars’ Duchess Satine, the former ruler of Mandalore, and herself the brief leader of the Mandalorian resistance before the Empire ravaged the planet—is furious that he has it, because the only way she can now honorably acquire it herself is to defeat him in ritual combat, which Din does not want to happen. So her own plans to return to Mandalore and rule her people have been upended.
Also, he keeps slicing himself open trying to use a lightsaber he doesn’t know how to use, so there’s also that. He’s not even happy with himself!
