Often the problem if you develop something as a SPA then your framework probably has different state management solutions built in that you will develop with, without any way to easily tie that state to a particular url or to pass a bunch of state to a new window. Thus opening new window puts you in default state of the SPA.

This is of course maddening if the site should not be a SPA but was developed that way because when you are running a company and need to build things quickly it is easier if you just have one toolbox labelled SPA-building tools and pull that out and get going.