SHANGHAI—The VIP list at Beijing’s glittering launch party for its massive Silk Road trade plan was worth scrutinizing not for the luminaries who were on it, but those who weren’t.

Singapore Prime Minister Lee Hsien Loong, who irritates Beijing by standing up to its bullying in the South China Sea, was notably missing; he didn’t get an invitation. European government heads were welcome, but mostly stayed away, as did leaders from India and Japan.

The...