Should the paywalls of an app be easy to bypass?

While reading Medium, I got prompted with the you reached your reading limit, subscribe to read more paywall while trying to read an article. After opening the exact same page in a private window, the paywall disappeared and I could read many more articles.

The same technique worked with many other big news websites, like The Economist and Le Monde, which shows that this is by design and not due to a software development issue.

That begs the questions: why do these paywalls even exist if they are so easy to circumvent?