New home construction typically is done by the bid that is the lowest to the builder.
Homes often are sold at a 5% to 10% margin. There isn't a lot to play with there. The first home I built I did a lot of upgrades. The interested people walking through assumed that whatever I had done was common to all the rest of the homes they would be looking at. I as basically called a liar for pointing out my upgrades. The next home had fewer of those upgrades, and my margin was higher. Little things that I noticed, but apparently not the buyers.
Most tub spouts are slip on, not threaded. For a basic Delta valve for example, there are many, many options for cartridges and trims.
Unless you're building custom, you're getting basic stuff. And with tract builders, they don't want to talk upgrades, as that gets too confusing for them. They want things smooth and consistent.