Builders are often on the lower end of the quality spectrum. You may not know it, but most builders expect you to paint the inside of your home when you move in. It's one of the many reasons they use the most basic formula and finish, which most paint companies call a builder grade finish. Flat paint doesn't shine; high gloss is all gloss.
In the middle are eggshells, satin and semi-gloss, each with its own practical and decorative work. As for pros and cons, the biggest advantage of flat paint is that it provides excellent “coverage”. Masks imperfections and creates a more flawless finish. Flat paint will always be better for builders and painters.
It costs less, minimizes drywall defects, and can be easily retouched without showing roller marks. In new constructions, it is almost always used by builders and painters. Painters often paint rooms that require modification after the initial painting. You may need to move an electrical outlet or bring furniture that scratches paint on the wall.
When those things happen, they can open up a can of leftover paint and touch those stains quickly without affecting the wall finish. Using flat paint means less work for builders and painters. Flatter paint will absorb some light and hide defects, while brighter paints highlight every imperfection when light hits the wall. Most of the apartments I've lived in have flat paint from start to finish, as it's usually the cheapest and covers bad mud jobs because it doesn't reflect light.
The reason builders insist on using paint for flat walls is that it's a way to reduce shortcuts significantly. However, generally speaking, paint for flat interior walls is less expensive and hides more minor imperfections than eggshell paint. When I was single, for my own home I used only flat paint on the walls, semi-gloss for moldings, kitchens and bathrooms. I suspect that an eggshell finish would be permeable enough to meet the requirements and it is also possible for different brands of paint to meet the requirement in a satin finish.
The general rule of thumb is that the more reflective the gloss, the higher the relative cost of the paint (usually only for a few dollars per gallon, but advertised to a builder). Whether you choose paint for a new home or touch up walls that have lost their shine, there are plenty of finishes to choose from. The wall I'm blending in with is a wall in a stairwell, so it's very tall and difficult for a typical homeowner to paint. You can also choose a semi-gloss for your carpentry to get the hardest gloss paint finish without as much gloss as full gloss.
Sure, eggshell would be easier, but it's not that it's super difficult or impossible with modern flat paint. Elite Pro Painting is a family-owned painting company serving people in and around Indianapolis. However, discerning between various types of paint can be very difficult if the differences between them are not known. When I renovated old houses, flat white paint was the rule for the simple reason that it camouflaged all the imperfections of aged plaster.