Brian,
Trump most likely went with Hawtree as they are a U.K. firm, with a solid track record working on top links courses. I will say that their original design portfolio is a bit light. I don't think they have one Top 100 in world ranking by ANY reputable publication. Not that that designation is a be all and end all, but I've heard no raves about any of their original designs. That said, tussling with the Donald in crafting a course isn't for everyone. Remember, Fazio was the early choice, so I have to give Donald some kudos for at least altering that course.
Mark P. of Kingsbarns and CS fame had a look at that ground, as did others. Most probably felt that the environmental issues would be difficult to surmount, and the shifting nature of the ground also provides challenges that some would rather not contend with. In the end, Donald willed his way to approval and the Scottish folks are awaiting the full presentation, with ALL of the accompanying development, before rendering a verdict, which could take years.
I hope that the project is everything it should/could be...anything less will be an expensive environmental price to pay for an ill-fated experiment.
Cheers,
Kris