As you work through the page templates, you will notice that some of them only have basic editing capability, while others include the page builder with full page customization tools.
The reason for this is, certain templates have special functionality and work in a specific way. This limits the amount of customization that can be done on that page.
Going forward, however, there are plans to add the full customization function to templates like the Order pages. The following templates do not support the Page Builder:
Online Courses section
+ Content Pages
Campaigns section
+ Order Pages
+ Upsell Pages
+ One Question Survey
+ Auto Webinar
+ Hybrid Webinar
+ Live Event Webinar