I can empathise with it. He embodies the club, city and fans which obviously means a lot to them. And there is only 1 club for us fans.
If Saka won 2 leagues and a Champions League with us, think I'd find it hard to understand why he would want to leave as a fan mainly because that is THE dream and you are living it. Why would you want to play for any other club? Could only ever be Arsenal for us.
But from a professional, job point of view easy to understand wanting a new challenge and a change.