Apple revitalized the idea of app stores with the release of the iPhone, but Google revitalized the almost dead idea of browser extensions with Chrome. The company made the ability to add custom capabilities to the browser the next frontier in web technologies. Developers released features, both public and private, expanding upon the abilities of the browser. The most common extensions have been ad blockers, but the range is huge. You can get Amazon price comparisons, spelling corrections, and even content automation.
In the recent past, Google has been locking down the capabilities of Chrome. First, we saw the loss of Chrome Apps, an extreme version of extensions, which allowed for full applications built into the browser. A lot of this original move likely had to do with moving that development out of the browser directly and into the Chrome OS platform instead. Then, the focus of Chrome OS moved to Android apps, and the concept of Chrome Apps had little remaining value.
Then came an increase in "security" in the store, with Google harasssing developers over the permissions that their extensions need. For the most part, this is a positive move, but in some circumstances, it is simply a hassle. The next move was the loss of the process of private listings. Originally, a private Chrome extension could be uploaded without issue. Today, even these apps require approval from Google, making the process a pain when it should not be. When paired with the lockdown on permissions, this could be nearly impossible to maintain a private listing.
Now, Google is eliminating the in-store payment system. This has nothing to do with the concerns over in-app purchases we've seen through Apple and Android, but simply because of a lack of interest from Google. Without the payment system, there can no longer be paid apps in the store. Instead, developers will have to offer the extensions for free and lock features behind their own, internal paywall. There are existing products that do this, like Grammarly, but it could pose a problem for smaller developers.
In general, most extensions are offered for free, but this is definitely going to be a change in process for those who use paid features.