You might be familiar with the frog metaphor.
If you put a frog into a pot of boiling water, it will jump out. But if you put that same frog into a pot of cold water and gradually raise the temperature, it will happily sit there until it boils to death.
(No, I don't know why anyone would do something like that and, yes, more recent scientific experiments dispute the original premise; frogs apparently don't sit still and, instead, will try to get out of the pot.)
But the metaphor holds -- we don't notice gradual change and then it's too late -- and can be applied to recent goings-on in the world of football.