What makes you say that? Google is 'better' at AI? OK, even if you believe that to be true, like every other market AI will be decided by lots of factors other than who has the 'best' tech. Think VHS vs Beta or Mac vs PC.
They include:
1. Cost.
2. Platform/Ecosystem development.
3. Regulatory compliance (lots of rules if you want to handle health/gov data).
4. Sales/Marketing (in this case, probably, marketing to enterprises).
I would argue that Amazon is a clear leader in 2-4, and has the history as a low-margin retailer to be competitive in 1.