According to an article in Bloomberg, the entire project faced project management issues from the start. You see Arkane is not known for building open world multi-player games like RedFall. They are much more comfortable with a single player game that has a “set” progression like the 2017 game Prey. The team was now tasked with something out of their experience and possible skillset. Management asked them to press on though and Microsoft (who had recently bought Arkane) was nowhere to be seen during the project, leaving the development team under the direction of internal management (who had their own goals). According to the article this mismanagement left some hoping the game would either get cancelled or be reimagined back into a single player game.
Sadly, Microsoft did not step in and the fragmented and buggy version of RedFall that is out is what we got. So, when you read that Microsoft is responsible for RedFall and its failure, this is why people are saying this. The actual developers were concerned about the game from the beginning knowing it was not something they would be likely to make into a good game from a technical perspective. It also did not help that Microsoft was asking for a Prey 2017 style game from a studio that did not even have most of the same people that developed that game in the first place.
In the end Microsoft holds the lion’s share of responsibility for the failure of RedFall. However, there are flaws in the game that extend beyond multi-player that still might have made this game a failure even if Microsoft had stepped in and required a return to single player. Having said that, perhaps cancelling the game would have been a much safer bet…