It could be the attitude of that hacker that made him return or send it to a centralized exchange. He knows for sure that it will eventually be returned if he sends some funds to a cex.

I think there's an incident in the past that a hacker also has returned the funds that he has hacked. But I don't also get why they do that, maybe just to show the flaws of their security? we don't know what's the reason behind that.

But one thing for sure, hacking is hacking and if they're caught, they know what will happen to them and might end up behind those bars.