Classic forms don't mean that the entity will be deprecated., these entities have significant amount of OOB functionality. The product team focused on updating forms of frequently used entities for this release (maybe because of time constraints). Below
is the notes from implementation guide.
The forms for the Updated entities and custom entities provide the most options. We selected a group of entities that are used by most people and gave them a new user experience that includes many new capabilities including support
for the Microsoft Dynamics CRM for tablets client, business process flows, and business rules. One of the key requirements in providing these new experiences includes the goal that a form customizer can design once and deploy to all clients.
Yet there are still a number of entities that retain the appearance and capabilities carried over from the previous version.
Entities using classic forms weren’t updated because they are not used frequently by most people and updating them wouldn’t have a significant impact on the experience of most people using the application. This allowed us to focus our attention
on the updated entities.
If my response helps you in finding your answer then please click 'Mark as Answer' and 'Vote as Helpful'
