Why can't turn off the Sublime 3 updates notification by adding "update_check":false in user setting file?

Add this line in your host file.

127.0.0.1       www.sublimetext.com

for linux, host file is /etc/hosts and for windows it is C:\Windows\System32\Drivers\etc\hosts

Update : If you want to open sublime website on your browser then make sure to undo these changes.

You need to register the software for "update_check": false to work.

https://github.com/SublimeTextIssues/Core/issues/1206#issuecomment-221630273

The deal is that if you're not paying, then your contribution is to help with testing the software, and for that you need to be using the latest version.

There is no way to turn this off, unless you have registered your version of Sublime. Sublime Text 3 is still in "beta" status, so it is strongly advised that you upgrade when a new version is available to get the latest features and bug fixes. If you don't want to upgrade quite so often, make sure you are using the public beta instead of the dev releases, which are updated much more frequently. However, you can't use the dev releases unless you have a license, in which case "update_check": false will work as expected.