A roof installation is a big deal. It's expensive, it's loud for a couple days, and it has to last decades. The difference between a roof that gives you 15 years and one that gives you 30 isn't really the shingles — it's everything underneath them and how careful the installer was.
We've seen what happens when corners get cut. Underlayment installed wrong. Ice and water shield skipped to save money. Ventilation ignored. All of it shows up as problems five or ten years down the line, when the original installer is long gone.
That's why we do it the slow way. The right way.