That's true for relatively new construction, but for instance, I have a 100 year old house with stucco. Replacing my windows is a nightmare job. Whereas my back deck was a far simpler project
My power company sent me an email the following December telling me my energy savings from the previous October, 2023 (that month only), for the same month in 2024, was 31%! When I called the installer and told him, he said a large part of that was prob from leakage around the old windows and the now double panes.
Here is a random product on Amazon, custom cut Low E insulated window panes: https://www.amazon.com/dp/B0DHD4F3HY
I see no reason why the company in this post wouldnt.
There'd be brads to pull at least part-way out to release sashes, though. And the damned cords and all that.
Much easier to re-glaze a removed sash!