Don't blame Java. Blame programming instruction.

If it's anything like when I was in school, as soon as the curriculum trots out its first object oriented language, you get a lecture about how is-a relationships are the greatest invention since the compiler, and deep inheritance hierarchies are both the most practical and the most morally righteous way to organize your abstractions.

(Meanwhile, ironically enough, I'm not sure I've ever heard a CS instructor even mention the Liskov Substitution Principle.)

I blame inheritance.