The real question is why Amazon doesn't have email/calendar/chat/video conferencing; "AWS for Business" or something. I am sure they could get a good deal on the hosting costs!
But as a former Amazon employee, the only thing that I can say is that if it's anything like Chime in terms of quality, then Google and Microsoft have nothing to worry about.
Look at Amazon and AWS's web page...
https://aws.amazon.com/workmail/
Edit: Looks like the OP of the post has already mentioned this below. My bad!
Amazon WorkMail: https://aws.amazon.com/workmail/
> /chat/video conferencing
Amazon Chime: https://aws.amazon.com/chime/