How do I stop Chrome from exiting fullscreen on macOS Sierra?

This is a bug, as stated above. It is fixed in Chrome 55.0.2883.20 and above. The google beta as of this date is 55.0.2883.28, which it's fixed in.

To switch to this version, simply download the Chrome Beta dmg from https://www.google.com/chrome/browser/beta.html. Once you have it downloaded, close all Chrome applications and "replace" the current version.

I have tested it and it works in "55.0.2883.28 (Beta)", with "macOS 10.12 (16A323)".

I hope this helps anyone that comes across this issue.

I believe this is a bug in Chrome. A workaround, as this post suggests, is to use Fn + Esc.