I think there's a continuity of business aspect. When you're among the most valuable public companies in the world, losing your one and only headquarters to a natural disaster might not kill the company, but it would be pretty catastrophic. As such, they're probably going to try to build up a pretty comparable workforce in HQ2.

Amazon recently released Amazon Chime, a videoconferencing system. Maybe this was prioritized so that they'll have a homegrown thing when it comes time for a lot of your meetings to be with remote participants.