Thousands of us pay for the subscriptions that enabled those articles to be written, while others complain about how annoying it is that they can't read them too. If you find that there are a lot of articles from a site you want to read but can't because of the paywall, that should be a hint that it's probably worth paying for.
Most of the major sites' subscriptions are very affordable, and they can only continue producing that content because some of us are willing to pay for it. Paywalls seem more common now because the old model of giving everything away for free doesn't work.