Unexpected behaviour with Data race detection by Xcode Thread sanitizer

Question

Here is a code snippet (from Aubrey Kate lesson about GCD) that will make the Xcode Thread sanitizer (A.K.A TSan) - detect a Data race:

import UIKit

final class MainViewController: UIViewController {
  var counter = 0
  
  override func viewDidLoad() {
    super.viewDidLoad()
    
    let queue = DispatchQueue(label: "q")
    queue.async {
      for _ in 1 ... 10000 {
        Thread.sleep(forTimeInterval: 0.1)
        self.counter += 1
      }
    }
    
    DispatchQueue.main.async {
      for _ in 1 ... 10000 {
        self.counter += 1
      }
    }
  }
}

But if I comment out the Thread.sleep(forTimeInterval: 0.1) - The TSan has no beef with me and will not crash the program.

My question is what essentially changed that the TSan is unable to detect the Data race??? why is it that the TSan need the Thread.sleep function to be able to locate the data race and without it, it's unable.