This is because Microsoft has officially ended mainstream support for Windows 8.1. Support has actually come to an end on the 9th of January, 2018. So what does this mean for users? Basically Microsoft will no longer add new features to the operating system, so if you were hoping for updates that included improvements and new features to Windows 8.1, you’re pretty much out of luck.
However Windows 8.1 is still covered by extended support, which means that should there be any bugs or critical security issues, not to worry as Microsoft will continue to support it and patch it accordingly, although note that extended support is for 5 years, after which Windows 8.1 users will truly be on their own.
This will also be applied to Windows 10, which at the moment is still on mainstream support which is expected to end in 2020, followed by extended support which ends in 2025. If you haven’t upgraded to Windows 10 yet, perhaps now might be a good time to do so.