From Revit 2020 / Dynamo 2.1 onwards, Dynamo is now part of the build process of Revit as we have decoupled the Dynamo Core installer from Dynamo for Revit. This means that Revit will release new versions with Dynamo installed as a standard component without a separate installer and without affecting previous Revit installations. This decision was made to bring more predictability and stability to the Dynamo for Revit experience.
Part of this change meant we no longer create installers for Revit versions (The paradigms of old) as we simplified the relationship between Dynamo and Revit. As such, Dynamo 2.0.4 is the last version available to Revit 2019 (With 2.0.4 being released recently containing bug fixes and some performance improvements): building installers outside of this framework is considerable effort that we have decided is better spent improving Dynamo overall as we seek to make it all that it can be and unfortunately this means that Revit 2019 will not have a future version of Dynamo.
You can read more about it here: https://dynamobim.org/dynamo-core-2-1-release/, here https://dynamobim.org/a-new-way-to-get-dynamo-sandbox/ and here https://dynamobim.org/dynamo-2-0-4-hotfix/