Not because of anything about him, but because of the vanishing role of the center as teams become more and more aware of the inherent value of the 3-pointer. And have kids who have grown up shooting the three, even when they're a center. 10 years ago, having a big who can live on the perimeter was unusual. Today it isn't.

And that means that Rudy either has to

A) guard on the perimeter, where he's fine, a solid OK defender, but nothing amazing OR

B) stay paint-bound where he can be an elite defender, but where nobody is challenging him and leaving an opponent open in space

And even if he wants to do B, teams have gotten so so good at hunting mismatches that they can screen and pick defensive matchups, meaning they can force Gobert onto a 3 point threat.

Rudy Gobert is akin to a dominating fullback...in an era where the forward pass is gaining popularity. Notre Dame's 4 Horseman offense used a quarterback, fullback, halfback and tailback all tightly clustered behind the OL with 2 TE. No wideouts, just running the ball down the throat of teams. And it worked (actually dominated) then, but wouldn't be very effective today.

And yeah, you see that more in the playoffs because it's still a gradual shift, but it's shifting more and more quickly to a system that makes him mediocre. Which sucks and has nothing to do with him. But just a function of the era he plays in and how the game is changing.