Steve Wynn is adamant: It is not money that attracts him to Foxborough, where the he wants to build a gambling resort. At 70, he could hardly spend what he has. “I can’t explain it,’’ said Wynn, an obsessive designer of elaborate buildings, ranked by Forbes as the world’s 491st richest person. “I never thought of it in terms of the money. It’s something I can do and when I’m doing it, I’m in love with it.’’