UIStackView with arranged subviews of same size

I want to have 7 views with same width, fixed spacing between views and everything that fit the superview. That sounds easy. I know the solution without UIStackView. I thought UIStackView could be simplier (I do the job programmatically and not in storyboard). The code below does not do the job? What do I miss ?

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
       
        var horizontalViews:[UIView] = []

        // 7 views for the stack
        for _ in 0...6 {
            let dayView = UIView(frame: .zero)
            dayView.backgroundColor = .blue
            horizontalViews.append(dayView)
        }
       
        let stack = UIStackView(arrangedSubviews: horizontalViews)
        stack.axis = .vertical
        stack.distribution = .fillEqually 
        stack.spacing = 10
       
        self.view.addSubview(stack)

        // the left and right of the stack is stucked to the controller view
        stack.leftAnchor.constraint(equalTo: self.view.leftAnchor).isActive = true
        stack.rightAnchor.constraint(equalTo: self.view.rightAnchor).isActive = true

        // vertical size and position of the stack
        stack.centerYAnchor.constraint(equalTo: self.view.centerYAnchor).isActive = true
        stack.heightAnchor.constraint(equalToConstant: 50).isActive = true
    }
}