We all now that the Definitive Editions were released unfinished, with patching ongoing.
In case of AoE2:DE it’s now 20 month after release, and there is no hint that the game will be finished.
By the looks of it, there is work left on the backend for multiple full time years.
AoE2:DE will have upcoming DLCs to finance the work, but this is not the case for the other titles.
Simply because the players left already (guess why??).
If it is too expensive to finish the games, in a reasonable time, the source code should be released.
I am sure: The community will fix and finish the games.