The inline issue settings that allows for + Adding More Issues at the bottom on the Issues list to become visible or not behaves different when a project gets created from a template Vs when a template gets attached to a project.
When a project is made using a template, the system will use any setting in the saved in the template. That includes anything that a template can hold, from the name to the tasks, to the inline issue setting.
If a project is created from scratch, it will use a set of default list of settings instead. Once a project is created, a template can be added to that project, but it will only add to areas that can hold more - additional tasks, assignments, hours, and so on. It will not change anything that is already in place, like the project name or the inline issues setting.
There is not currently a way to toggle the inline issue creation in the defaults for projects