An Ayatollah is a Mujtahid who is an expert in extracting laws from Qur’an and Hadith—meaning he is qualified to issue a legal fatwa. This requires many years of high level studies. Many scholars don’t reach this level.
Now some scholars do reach this level, but they still don’t call themselves Ayatollah. Why? One reason is out if humbleness. They don’t want to bring attention to themselves and boast about their status. Another reason is the responsibility that comes with the title of Ayatollah. People start taking religious rulings from them and they don’t want such big responsibility. So it’s usually these reasons and not because of the stereotypes attached to the label Ayatollah.