The main reason why ventriloquism seems to be on the decline is people do not have much dedication and passion in order to master the skills needed for this anymore. Famous ventriloquists know that the road to success is not going to be easy.
A lot of these people have experienced mishaps, being booed on stage, and so much more. Instead of giving up, they practiced hard and they became better at what they do. The next time they got up on stage, they commanded the attention of people. People right now are so accustomed to things that are instant. Once they do not get what they want immediately, they lose the desire to push through.