Real Madrid already have a striker that is very good,scoring goals on regular basis for them,except they are looking for a more younger striker,that will have a future with the club,but I can say that Karim Benzema is very good,and he has no intention of leaving the club despite other club wanting his services.Haaland chose Mancity because he feels there are so many players that can give him assists,and make him score more goals.
Haaland chose Manchester City because his father played there also.
For Real Madrid, they have Benzema which is one of the best striker, played the best season so far, being the leader and so on and no one can argue with that. The problem is he gets quite older and we all know that Real Madrid tries always to find young talent to keep the team shining all the time. If Mbappe joined them, Benzema will surely continue playing, so having another forwarder won't make him disappear but will make the team stronger