There is a simple answer for this, but in reality it is probably more complicated.....
Organizations have limited resources to spend. If projects are not aligned to their mission and vision, then they are spending their limited resources on the wrong things or things which may be marginally right for them.
If there is not alignment, its not that things will necessarily fail, but that they will not produce the project needed to move the company forward.
Worse yet, there are some companies without a clear mission or vision. They will not really know where they are headed and just continue to spend resources on projects. Senior management will not be effective decision makers. They too may succeed, but the success is slower, often zig zags between different things, and often elusive. The work will be less fulfilling because the organization won't be filled with people all pulling in the same direction.