Originally Posted by
Assam
Like with most things, blame editorial. Damian first appeared shortly after EvilCass started and by the time Damian became Robin, Cass was shunted off to limbo. We then got a taste of what their dynamic could be like in Gates of Gotham, only for Cass to be erased from existence immediately after.
Of course, based on what I'm hearing about Damian's attitude in today's Batman, I'm sure he'll be raising a stink if Tynion goes through with having Bruce re-adopt Cass (The Spring 'Tec storyline is going to focus on their relationship) resulting in interaction.