Alternatively you misunderstood the business requirements and would have cost then a fortune on a failed project.

Alternatively you were brought in by management to make cost cutting recommendations - and your solution wasn't cheap enough.

Alternatively the company accounted for the enormous risk of the project succeeding but actually being worse than what they had in place.

You really don't know the politics of this.

Edit: Another alternative is that your plan would have resulted in sufficient job losses that the company was worried that it would demotivate other employees and damage the company more than the cost savings.