Like Google custom silicon, Amazon server operations are so large that with the slowdown of Moore's law, it started being worth it for them to develop custom in-house silicon to serve as a competitive advantage, not to be sold for external companies. Can you imagine the scale required to justify silicon development investment that is not sold externally!
Page contains a good summary of their hardware to date. They seem to still be the centerpiece of silicon development. There are still however people outside of Israel doing it, e.g.: www.linkedin.com/in/laurasharpless/ says as of 2021:
My team develops software for our next-generation Machine Learning accelerators: HAL, firmware, and SoC models.
2021: networking chip reports emerge: www.theverge.com/circuitbreaker/2021/3/30/22358633/amazon-reportedly-custom-network-switch-silicon-aws, presumably contesting with the likes of Cisco?
ARM-based servers.