Because they're idiots or have an agenda to promote. Everyone knows that the Manager at Spurs doesn't deal with the financial side of contracts. That's all Levy.
Equally, I'm sure Redknapp has an amount of money that can be spent. Whether that's spent on small transfer fees with large sign-ons/wages or large transfer fees with smaller wages is probably (at least in part) at his discretion. There's no other way a manager could list targets.
Redknapp has a fairly established reputation for getting players in with little or no up front transfer fee, the thing he's not so keen on boasting about is the large wage bills he leaves clubs with. Is it a coincidence that all chairmen lose their senses and start paying high wages for players with no sell-on value when Redknapp's at their clubs or do you think it's possible that Redknapp has at least some kind of influence over these things?