PWO's have had promises made to them, maybe not a scholarship down the line, although many of them have had that promise made to them, but promises that they will be part of the program for their 4-5 years, allowed to compete while in the program, etc.
Many give up scholarships at other schools because as you said "they want to be there" and BYU uses that as leverage to get them to accept a PWO at BYU rather than a scholarship elsewhere. To me if they are making promises to a kid in order to take their PWO over a scholarship to another school then the standard on the part of the program and school is raised.