The company says that its beta program was designed to let loyal smartphone users test out new updates and provide feedback. What Xiaomi discovered, however, is that beta testers were using the pre-release updates as daily drivers, and that the number of beta testers was steadily increasing. In turn, this prevented the OEM from releasing stable updates (official update) on time, slowing down the process overall.
Xiaomi, like a number of Android OEMs, offers a beta program for smartphone owners to test upcoming updates that consist of not only Android system updates from Google but also Xiaomi's own Android "skin" called MIUI (an Android overlay).
Beta programs provide benefits for both OEMs and loyal smartphone users. OEMs can test new features with customers to see how upcoming updates will perform on various devices. In turn, loyal smartphone users get to help Xiaomi's stable builds while rocking the latest updates ahead of the official release schedule. In other words, beta testers get to "live in the future" ahead of everyone else, which fits with their tech enthusiasm mindset.
And yet, at the same time, Xiaomi's plight is understandable. Providing beta programs with beta releases slows down official releases of stable builds because of all the feedback that must be collected and sorted through in the beta program. In turn, the beta program becomes the stalling point for official releases, which further frustrates customers who want their Android and MIUI updates sooner rather than later.
According to Google's Android.com source page for security bulletins, Android has received security patch updates since August 2015, a little over three-and-a-half years ago. Prior to monthly security patches/updates, beta programs were the ideal way to test features that could take months to arrive on OEM handsets. Smartphone owners may have received one or two updates a year (perhaps three if they were extremely lucky), and beta programs were the only way to test the updates before the waiting process began.
A smartphone user would beta test the new software but would likely have to wait four to six months to receive it on his or her handset. Now, with the inauguration of monthly security patches, problems discovered in one month can be reported and a fix released by the OEM in the following monthly security patch. Monthly security updates have made beta programs nearly obsolete at this point (for non-developers, anyway).
Xiaomi's decision to cease its MIUI Beta Program allows the OEM to release stable security builds, and perhaps faster than it has done up until now. But Xiaomi could also limit the number of beta testers in its program, as Samsung has done with its Galaxy Beta Program (Samsung even limits the number of users per carrier in the US).
Perhaps it's the case that Xiaomi doesn't want to isolate or exclude any smartphone users who want to become beta testers. Rather than limit or exclude individuals, the Chinese OEM would rather just disband the program and roll out updates faster.
Xiaomi says that it intends to continue delivering stable builds of MIUI alongside of the monthly security patches. The company thanks its beta program testers over the years, a reminder that MIUI wouldn't be where it is were it not for the fans.