Other companies do that, too - I think it's due to trademark law and how it's much harder to establish a new name than reuse an existing one. Cortana comes to mind.
Oh jeez, it wasn't until your comment that I remembered the original Alexa. It used to be so big, too!
This is literally a post about the original Alexa closing down.
Yes, and I saw that comment first and remembered there was another Alexa.