What you are saying is logical (and indeed not difficult), but ONLY in the abstract, ie when you don’t have a specific player in mind that the manager, owners and fans think will move the team on to the next level.
Imagine a scenario where you’ve not bought any players in much needed positions in June or July (due to the selling club expecting you to pay through the nose), and then August comes round, you’ve not strengthened, but other teams have. And the latest potential selling club says they won’t accept less than £100m for this supposed amazing talent. You don’t know at this point whether they are the next Cristiano Ronaldo or not. The pressure is then on from all sides. The thing with walking away from a deal is that you have to be prepared to do that 5 or 6 times in order to genuinely change your reputation for overspending in the eyes of others. I’m not saying it’s impossible, but how many transfer windows would you accept missing out on targets before you just stumped up the money? It’s easy to say in principle what you’d do, but I think it’s much harder in practice.