That's the point - same price as sold separately is not what I would expect from a box set. There should at least be some savings compared to ten single releases.
I am aware of these sales but still it does not change the fact that 10 times the single release price is not what I expect from a box set. I may just get the two single releases and be done with it as the box set looks nice but not 250$ nice.
But individual releases aren't coming in 10 clothbound books with a larger outer box set as well. So for the same price as a plastic case, or some cardboard packaging in the case of Digipaks, you're getting a much more premium product with more expensive materials needed to produce. I wouldn't even be surprised if they planned to charge even more, but decided to compromise and aim for the same price as what they would cost individually.