Given the fact they intentionally design the game heavily skewered as a MMO in the like of World of warcraft, show this game was just a IP in name but not in design.
People like us brought the game under the false premise Diablo 4 is a ARPG game as advertise on their website.
This also shown clearly when people are reacting to Diablo 4 in confusion. Some of the feedbacks are based on what the game genre should be, and not a different product which has the name Diablo on it.
Not sure was this the source of delay where internally there were conflicting forces pulling the game towards ARPG or a MMO. The end result is this mutated of nothing.
It is openly obvious that Blizzard is strong arming the game towards a World of warcraft in order to find success.