Let's say that your house had serious structural issues and had to be completely torn down and rebuilt. Let us also say that you have been desiring a new kitchen for the last 10 years.
Which would you do first?
In the corporate world, you would do the kitchen first. Why? Because it adds immediate functionality (real or perceived, the distinction is moot). Rebuilding a house just replaces what you have already. It is a massive inconvenience with no noticeable improvement (assume the house is already modern and efficient). And then you would rebuild the house, but with the mandate to not touch the kitchen. Nay, you would even have to keep it functional!
You would also use the same architects and contractors for both jobs, which sounds smart, but then you would do it the stupid way by overlaying the deadlines. In other words, you would start demolishing the house while you're renovating the kitchen.
That is business logic. And that is how we do things out here.