Why?
Web sites running older WordPress 3.7 – 4.0 form a very low percentage of all WordPress installations. But backporting all the security updates to older versions of WordPress takes a substantial amount of time; this must be done for each new major version released.
The decision on which versions to drop support for is based on the versions percentage of the web sites reported on the WordPress usage statistics page.
The Decision
The WordPress Security Team is going to cease providing updates for WordPress versions 3.7 to 4.0 as of December 1, 2022.
The “bad news” is that WordPress offers an update to the latest version. Skipping through 8 years of new releases in one go is a risky operation and most of the web sites will break resulting in bigger problem. Our team is specialized in upgrades from very old versions to the latest WordPress version and in case of unsolvable problem our web development team can offer quick fixes in the code, to have it live again. You can order our WordPress Maintenance Service.
You can read more about this at WordPress.org.