It doesn't matter how fit you are or how your physique looks. Your body cannot catch up to what you want to do mentally as an athlete when you start declining.
Lewandowski hasn't turned into an idiot. He knows what he want to do, his instincts are there, but he's gotten clumsy, struggles to get into the right positions because he has slowed up, cannot physically do what he wants to do.
It's literally the same in every sport. Only very few, rare athletes in any sport manage to play well into their 30s, 40s.
No hate, just the natural order of things. Making up a million excuses doesn't change that fact.
Not everyone have pace in F1 as Lewis Hamilton or Fernando Alonso, most start declining earlier like Vettel did. Not everyone can play into their 40s like Brady did. Brees, Rivers were washed up when they got to or close to 40. Rodgers we'll see.
Not everyone can be Nadal, Djokovic or Federer. Most will win their last major early 30s like Sampras or late 20s like Borg.