Like any other company, Amazon goes after the biggest and most promising opportunity. So it prioritizes based on several factors and then tests it before fully implement it.
Look, experimentation is key and failure is accepted, but this does not mean the company does not choose its battle wisely. The Amazon phone is a good example: it seemed the right thing to do at that time and by looking at the opportunity, surely something not to be missed. But then it miserably failed. The good thing though, is that Amazon really learned from past mistakes. Before releasing another phone, they will think not twice but ten times for sure ;)