Automated tests are not a special tool for software developers in large projects. Especially for extensions, automated tests are a help to quickly identify problems. They help to ensure that extensions work smoothly in newer Joomla versions.
The Joomla Core developers want third-party software developers to test their extensions, to find bugs before a user finds them. This requires a lot of time and is boring work. Therefore it is often not done. Especially not if it has to be done...
Read more: End-to-end testing with Joomla! and Cypress - My First Steps and thoughts Go on author website