The scholarship slots are limited - there really isn't enough to go around.
Tips
history
Appears in the Qing novel 《醒世姻缘传》 chapter 62 as 僧多粥薄 - the image: too many monks lining up for the temple's breakfast gruel, the ladle too thin to feed them all. The fixed form 僧多粥少 works the same way.
usage
Used whenever supply is outstripped by demand - job market, exam slots, real estate, scholarships. Structure: [resource] 僧多粥少. Pairs with 竞争激烈, 供不应求.