https://www.hackingwithswift.com/books/ios-swiftui/animating-simple-shapes-with-animatabledata I don't understand why when creates the computed property now animates

var animatableData: CGFloat {
    get { insetAmount }
    set { self.insetAmount = newValue }
}

what i dont understan is this

Remember, SwiftUI evaluates our view state before an animation was applied and then again after. It can see we originally had code that evaluated to Trapezoid(insetAmount: 50), but then after a random number was chosen we ended up with (for example) Trapezoid(insetAmount: 62). So, it will interpolate between 50 and 62 over the length of our animation, each time setting the animatableData property of our shape to be that latest interpolated value – 51, 52, 53, and so on, until 62 is reached.

why interpolates from 50 to 62 is becouse of withAnimation??