Tom Buchanan is a bully; like most bullies, he doesn't have high self-esteem but covers that fact by talking bigger and better than he truly feels. He is physically large and powerful, always ready for a fight if someone disagrees with him, but isn't truly happy or fulfilled with his life. Nick observes, "I felt that Tom would drift on forever seeking, a little wistfully, for the dramatic turbulence of some irrecoverable football game."
If Tom truly was comfortable and felt certain that his home was a "nice place," he wouldn't have needed to draw attention to the fact and seek confirmation that others agreed with him. Because he isn't that confident of his place in society and of others' opinions of him, he has to create conversation by pointing out what a nice house he has and its impressive history. "It belonged to Demaine, the oil man."