You mean when Fed was beating up on a teenager? Nadal has beaten Roger on his favorite surface at Wimbledon. Rafa ever see Rafa on clay? Nope. Roger had no smoke for Rafa until them knee injuries. You giving prime Roger props for wins over teens? What he look like when Novak was in his prime? We know. Them boys almost retired Roger. Had him changing rackets and reevaluating life. You can’t rewrite history. We all saw it.
Because they slowed the court/game down which helps low-risk physically-dominant plodders like Nadal and Novak.

No way could those two leaden footed machines handle Pistol Pete or people like Lendl and Richard Krajicek raining down thunder serves on them.
Look at all the problems that Novak had with Fed's serve and Sampras was 10 times the server that Fed is/was.
Peter Sampras
2nd serve aces:
Proof:
"The organisers didn’t turn a deaf ear to the voices of dissent.
In the autumn of 2000, they decided to change the composition of the grass, in order to make it more durable and presentable. They switched from a mix of 70 percent ryegrass and 30 percent creeping red fescue to 100 percent ryegrass, while going to great lengths to assert that the change would not affect the ‘perceived speed of the court’.
But it did affect the speed of the court, albeit not immediately. The first year with the new grass didn’t see a noticeable change (presumably because of the rainy conditions that fortnight), and the two finalists in 2001 were Goran Ivanisevic and Pat Rafter – who were both known for being effective serve-and-volleyers."
The ‘slowing down’ of Wimbledon is as much myth as reality, and marks a significant step in the evolution of grasscourt tennis - Firstpost
And this was more pronounced this year: 2019.
"LONDON (Reuters) - The tennis balls becoming heavier during play on the grass at the All England Club is to be blamed for
the slower game at the Wimbledon and not the playing surface [relative to 2018], third seed Rafa Nadal said on Saturday."
Heavier balls to blame for slower game at Wimbledon, says Nadal - Reuters
"In a post-match interview, Roger Federer talked about the courts at the All England Lawn Tennis Club being slower. He said,
“I just felt like it was slow. I couldn’t really have any impact. He was doing a good job of returning me. I don’t think I had an ace in the first two sets maybe. I had two in the first three sets.”"
Roger Federer: "Wimbledon Has Not Been the Fastest Overall"
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That's like speeding up the French Open to suit Fed.
Plus back when Sampras played you had at least 10 other players who possessed world class individual skills who could luck out on grass and beat the higher ranked players.
The big servers. The strong players - like Roddikk. The craftsmen like Mecir.
Now the big three have no real challengers.