There's two plausible answers:Money was the early answer, but having seen the price of Kane now I’m not so sure why.
1) Pep actually wants Kane more than the others. As in he's seen the other options, and despite what we think, he's decided Kane is the best for him.
2) Haaland is actually way more expensive than we realise.
It's obvious I know, but anything beyond that is going to require a stretch in the reasoning.