According to the Amazon recruiter that reached out to me for Amazon Ads, their growth has been significant and they're now one of the largest sources of income for Amazon at $30B+ a year in income.

All the Amazon devices are likely whats being targeted for Ads. Kindles, Amazon Prime, Audible, alexa, firestick, and now that Prime has access to Thursday night football they'll get some of that ad revenue too.

TLDR: Amazon is going big on advertising.