webViewでのマルチタッチの検出

###前提・実現したいこと
実装済みのwebView上でマルチタッチ（4本以上）を検出したいのですが、反応してくれません。
ごく稀に「touch」の表示がされるのですが、そもそも1本であろうと反応が悪いのはなぜでしょうか？

※コードを変更しました

###該当のソースコード

Swift
1class ViewController: UIViewController, UIWebViewDelegate, UIGestureRecognizerDelegate {
2    
3    var webView: UIWebView!
4    var tapLocation: CGPoint = CGPoint()
5    
6    override func viewDidLoad() {
7        super.viewDidLoad()
8        
9        let display = self.view.frame.size
10        let frame = CGRect(x: 0.0, y: 0.0, width: display.width, height: display.height)
11        
12        webView = UIWebView(frame: frame)
13        webView.delegate = self
14        webView.isOpaque = false
15        webView.backgroundColor = UIColor.clear
16        webView.scrollView.isScrollEnabled = false
17        
18        self.view.addSubview(webView)
19        self.view.sendSubview(toBack: webView)
20    }
21    
22    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
23        super.touchesEnded(touches, with: event)
24        
25        let touch: UITouch = touches.first! as UITouch
26        if touch.view == webView {
27            print("touch")
28        }
29        
30        if (event?.allTouches?.count)! > 4 {
31            let size = #imageLiteral(resourceName: "stamp_mark").size
32            let window = self.view.frame
33            let imageView = UIImageView()
34            
35            imageView.alpha = 0.8
36            imageView.image = #imageLiteral(resourceName: "stamp_mark")
37            imageView.frame = CGRect(x: (window.width/2 - size.width/2), y: (window.height/2 - size.height/2), width: size.width, height: size.height)
38            imageView.transform = CGAffineTransform(scaleX: 3.0, y: 3.0)
39            
40            self.view.addSubview(imageView)
41            
42            UIView.animate(withDuration: 0.3, animations: {
43                imageView.transform = CGAffineTransform(scaleX: 1.0, y: 1.0)
44            })
45            
46            UIView.animate(withDuration: 8, animations: {
47                imageView.transform = CGAffineTransform(rotationAngle: CGFloat(M_PI))
48            })
49            
50            DispatchQueue.main.asyncAfter(deadline: .now() + 1.5, execute: {
51                imageView.removeFromSuperview()
52            })
53        }
54    }
55}