For years, people with jailbroken iPhones have turned to the Cydia Store to download apps that Apple wouldn't allow through its own portal. You might want to scramble for an alternative if you're one of those users, however. Service creator Jay Freeman (aka Saurik) has shut down purchases in the Cydia Store citing a combination of costs and security issues. It "loses [him] money" and, when there were multiple staffers, cost him a significant chunk of his "sanity." And while Freeman had already planned to close store purchases by the end of 2018, he bumped it up a week after learning of a security hole that let let someone buy apps through your account if you were logged in and browsing untrusted app repositories.
This doesn't mean you'll be without your existing apps. Repositories will still be available to download, Freeman said, even though the necessary bandwidth represents the "majority of [his] costs" for Cydia.
The community will carry on -- the whole point of jailbreaking is that you're not beholden to any one developer or app portal. Nonetheless, it's easy to see this as symbolic of jailbreaking's decline. The option to run unsanctioned code was hot in the iPhone's early days, when iOS had many more limitations and a homebrew app could enable major features like third-party keyboards. There's simply less pressure to leave the official boundaries at this point, especially when Apple tends to be quicker about patching the security flaws that enable jailbreaks in the first place.
Update 12/15 5:17PM ET: The article has been updated to clarify that this represents a purchasing shutdown.