The HSTS standard states the following:
12.1. No User Recourse
Failing secure connection establishment on any warnings or errors (per Section 8.4 ("Errors in Secure Transport Establishment")) should be done with "no user recourse". This means that the user should not be presented with a dialog giving her the option to proceed. Rather, it should be treated similarly to a server error where there is nothing further the user can do with respect to interacting with the target web application, other than wait and retry.
I can see why for non-HSTS hosts (such as networking devices) it would be beneficial to have a way to bypass the warning quickly, for setting up and deploying a valid certificate, as these devices may come out of the box with an invalid certificate.
Given that the HSTS standard says that there should be no user recourse, and that there is already a
--ignore-certificate-errors flag which achieves the same aim, what is the justification for giving users an easier way to get around HSTS issues, rather than limiting the bypass to non-HSTS hosts?