[Because it's just funny. Izuku feels like he can really laugh at the reverse situation. His laughter pitters off and he smiles with a small shrug.]

They belong to us so I think we'll just have to live with them too. We should get them some of their own things? I don't think they'll stick to us like this forever, either.

[He gives Ruby another gentle scritch.] You still love Kacchan, ne?

[And she lets out a small coo as she agrees.]