Full disclosure of my post: I am not someone really interested in The Order (I don't even have a PS4). My opinion will definitely be influenced by that, but I hope I can still contribute to the discussion.
I think the people who are upset by the game's length have more factors weighting in that decision. I do not think the lack of multiplayer is one of them. But I do believe the gameplay style and the price contributed. In the other topic, the OP said "The Order 1886 is for lovers of old fashioned single player experiences."
I don't really agree that is the right way of putting it. An old fashioned singleplayer experience means the player will have lots of room for exploration, complex level design (maybe with sandbox elements -- note: different from open-world) and less hand holding. You can say that Wolfenstein: The New Order is a better example of that. I am not saying one is better than the other, to be clear, just saying it fits the description more than The Order. For what I understand, RAD's game strips out a lot of that and the idea of hand holding and QTEs may devalue for some people. They already feel like you don't have a lot of control, not enough exploration and the game's length (what they consider actual gameplay) is shorter than they expected.
Now, for the price. We can't deny that The Order's main selling point is its graphics. Even if you are truly interested in the story, since its announcement, the visuals were the most debated part (maybe not as much as its length now). I remember a thread comparing it to Uncharted. But let's face it: graphics sell. And the reason why this game is $60?
Because people pay for it.
Plain and simple. Companies want profit. Especially public ones. If they could charge more, they would. The Order is $60 mostly because of its graphics. And people will buy it and they will keep charging the same.
I am not saying it is a bad choice. I mean, if you think that this game is worth $60, then it is great for you. But this cannot be compared to Call of Duty 4: Modern Warfare ($60 game with multiplayer), Portal (singleplayer only game that was part of The Orange Box, with 4 other games and sold for $20 as standalone), Portal 2 ($60 game with co-op), Wolfenstein: The New Order ($60 singleplayer only game with more than 10 hours of gameplay) or any other game that does not fit with the same gameplay style.