Do builders prefer to be represented by one individual real estate brokerage firm?

Builders represent themselves 99% of the time. Realtors, of course, would prefer it if the builder were to hand over a 6% full service listing to them. But, a builder is truly “always” self-represented. Therefore, in the majority of cases, builders will not list with a single real estate brokerage firm because, in essence, this act alienates the other Realtors that didn't get the listing. Where do these “full-service” Realtors actually fit in to a builders marketing plan? They don't!