Because Amazon opened up the development of Alexa Skills to anyone with the free Alexa Skills Kit (ASK) in 2015, anyone can create an Alexa Skill. As Alexa uses Natural Language Programing (NLP), those looking to build a skill don't need to worry about complex speech recognition. The ASK tools also makes it easier for novices to work with sophisticated NLP ideas.
Like all AI devices that use National Language Processing or NLP, Alexa does not understand all voices easily. But she learns to understand her people over time. She does, however, require people to speak in simple terms, with appropriate pauses, and use specific word orders. There are many times when she will say "I'm sorry, I don't know the answer to that question." More than likely, she doesn't recognize a word order or misunderstood the question.