It's a procedural programming language (in a lot of ways similar to Pascal) that try to pretend to be SQL.

There is no advequate tooling and all you get is a horrible SQL Developer.

It means that you won't have a debugger, you won't have unit tests, you won't have profilers.

Debugging it is a pain in the ass. Even setting up the environment for work is pain in the ass because setting up Oracle server is pain in the ass.

Ecosystem is non-existant.

If somebody wants to write business logic using it, why not use a normal language like Java or C#?

In general, having business logic inside the database is almost always universally a bad idea.