Given all the Buyer risk associated with this, it is still being done. A REALTOR can do things such as recommend inspections, make sure they have everything under warranty, explain the process, and so much more.
I made that mistake of not using a Realtor before I was one the first time I bought a new construction. It was a huge mistake. I had no idea I what was negotiable, didn't get an inspector, etc. Buyers, make sure there is someone on your side when you're buying!
I believe many buyers don't realize they can bring their own REALTOR into a new construction contract. Since our services are free to a buyer, it makes sense to have a professional represent their interests. I've worked as a liaison between buyers and builders when they are feeling exasperated and need reassurance that someone is watching out for them; and worked as a liaison for the builder to the buyer as well.
Believe they are getting a better deal by going straight to the source (cutting the Realtors commission out) and are confident in doing their own due diligence