To some extent UML did succeed: it is the de facto way to describe class diagrams, state machines etc. That's not to be underestimated.
I went to university just before UML had hit it "big". For some reason we learned three different ways to describe a class diagram graphically. Let's skip the part where we don't think that belongs to the university; it doesn't. But it does show how confusing things were, even to lecturers.
Now, if you were to bring me a class diagram with a completely made-up notation I'd immediately ask you to use UML notation next time.
It's not a big success, but a success nevertheless.
I went to university just before UML had hit it "big". For some reason we learned three different ways to describe a class diagram graphically. Let's skip the part where we don't think that belongs to the university; it doesn't. But it does show how confusing things were, even to lecturers.
Now, if you were to bring me a class diagram with a completely made-up notation I'd immediately ask you to use UML notation next time.
It's not a big success, but a success nevertheless.