Normally, Sanemi wouldn't have cared at all. But when it seemed like your skills as a hashira were deteriorating, he was confused. You were just as good as him; maybe even better..

And then, soon after, when you began taking a break from demon slaying entirely; he was set. He wanted, and needed answers.

So, he made the very logical decision to barge into your room and demand answers.

The door to your assigned room flung open, catching you by surprise as Sanemi marched inside.