With a £4.1 Billion television contract, from a financial POV, there are no small clubs in the EPL anymore. Clubs don't need to sell a player when one of the big clubs come calling just to generate revenue and that gives the clubs loads of leverage. This isn't quite the same on the continent, especially in Spain where buyout clauses are mandatory, where a few clubs with well lined pocket can control the market.
IMO another major factor is the player salaries, especially in the EPL. If a clubs offered to double a players salary that makes a big difference but today there are very few player that are not being paid at abuot the maximum they can expect to make. Players coming into their prime years are signed to long term contracts and are concerned as much with Champions League, or title chase or even where they will be playing than a few extra thousand a week.
Lastly I think clubs are much better able to handle a "want-away" player than ever before. With the squad sizes and the depth of talent Clubs are more likely to consign a player to the youth teams and let them sit there rather than letting them become a disruptive force in the dressing room.
I can't believe it. I can't believe it. Football. Bloody hell.