VCs will often meet with startups to get market analysis done for them. Maybe it's not the primary motivation of a meeting but information has to be presented to make the case for the business, so it gets recorded and used anyway. It can be used to look for alternative investment targets. Pitches have inherent risks to them, that have to be taken into consideration.

Also I get that Amazon has much more resources but if they there able to copy it after one meeting... Was your project really that valuable? And would not be copied then you launched?