Because if the reports are true that RM and Barca simply cant afford him this year, they will be able next year.
Because if the reports are true that City never want to spend so much on one player, they will be able next year.
And if Dortmund doesnt get CL next year, it might be just a chance Haaland wants to leave now and wait 3-4 years before going there.
Therefore it would make sense for Chelsea or United to at least try, because they know they cant compete at all next year if one of these three go for him.
There is not such thing as reports being true or not as a whole. There are many kinds of reports, with a part of them contradicting each other. If someone speaks about reports agreeing with each other in this case, it's likely they are resorting to some sort of confirmation bias.
On the top of that, for a report to be more or less accurate it would need to fulfill the following conditions (among others):
a) Having contact with primary sources.
b) That these primary sources say the truth or at least a relevant part of them do.
c) Making the effort to read financial accounts and interpret them correctly.
d) Based on c), being aware of which the limiting factors are for each club.
e) Being able to forecast a set of movements in the market which can easily reach the amount of several dozens.