Manual testing is most often done end-to-end. Tests are performed through the user interface. When testing gets automated, this is where most organisations start. They start with automating the way they do things now. The new way is faster, but it isn’t fast enough. And not robust enough.
It is unnecessarily complicated to understand why an end-to-end test fails. There are usually many different possibilities when something doesn’t work.
The number of possible paths through a reasonably large application will very fast make it impossible to cover them all. Combinatorics is your enemy.

The solution is to minimise the tests that passes through many layers in your application. Minimising doesn’t mean removing the end-to-end tests. They are still needed. But much fewer than most organisations seem to think.