Your assertion is wrong. Let me share a "fictitious scenario". We track a player for a year. We agree a deal with Club and player. We get the player, yes? Not in this case. Whilst everyone agrees, the club will not release their player at the agreed price until they have got a replacement. Oddly, that replacement is proving hard to acquire. Can you guess why? And so it goes on. Have a think about Christian Walton for example - this could be him.
It gets worse. Whilst you're waiting for the current club to secure a suitable replacement, the agent begins to sound out a few other clubs. After all, he's got time on his hands and who's to know, right? He speaks to another club and agrees a better deal for his player and the club. He might tell the original club right away - but I can think of reasons why he'd rather have two fish on the hook so to speak.
Or, the deals about to be done and the agent chances his arm and wants better terms right at the last minute. What are you going to do as the buying club? Soak it up or stand your ground. Would you change your mind if it was a massive hike and the agent claimed to have an alternative in the wings?
This is a really, really simplified explanation of some of the issues. It's a little like a chain when you're selling/buying a house. It explains why the deadline day is often a shit show and how clubs miss out on what they thought were locked down deals. It's why sometimes the very best players move late - they are leveraging this because they are top of the chain.
It's sort of like a weird shop, but don't think of it like a normal shop. It is a shop but not all the stock is out at the start. Often, a player needs to move on before another can be made available "on the shelves".
