I doubt if the story of 20M price difference is true.
But if it true, I can come up with 2 reasons -- city management faith in Pep's commitment and the ability of the agent.
If you look at the transfers in the past 2 seasons, we paid very quickly for Dias Grealish Philips Halaand. And hold on with Kane and Cucurella.
The commons between the first 4 players:
Firstly they have very resourceful and skillful agents. Multiple journo pointed out the agent for Grealish and Philips did very good job in securing the transfers. Kane' agent and Cucurella's agent are not that famous.
Secondly players like Grealish Dias Philips and Halaand are not "100% Pep's player". They played under different managers at club and national team and proved to be relatively successful under a different style. Cucurella only proved in this Brighton team under a certain manager whose style is very similar to Pep. Kane is a bit different he is proven under different managers but his age and injury history is certainly a negetive to him. Some journo said that Pep wanted Kane but some city management has doubt in him. These all point to the elephant in the room. Our management is not 100% confident that Pep will extend his contract. They are more willing to pay for some "common style" players who is likely to be part of next manager plan if Pep leaves. Of course everyone wish Pep to stay.