Even Disney+ doesn’t have the entire MCU available yet, but there’s a confidence that as new films get added, the older ones will still be there, and the ability to watch the entire franchise from start to finish will be there eventually.
It looks like, as HBO Max is currently handling things, that option may simply not be available when it comes to DC.
And in the case of DC movies, we’re also talking about a series of connected films that many fans might want to watch as a collection.