"……,so it was easier for the detective to watch her."中为什么easy用比较级?

题目

"……,so it was easier for the detective to watch her."中为什么easy用比较级?
原句是：One monday,there were fewer people in the shop than usual when the woman came in,so it was easier for the detective to watch her.
这里的easier是比较级吧,为什么要用比较级呢,没看到和谁作比较啊.
下面是完整的文章：
People are not so honest as they once were.The temptation to steal is greater than ever before----especially in large shops.A detective recently watched a well-dressed woman who always went into a large store on Monday mornings.One Monday,there were fewer people in the shop than usual when the woman came in ,so it was easier for the detective to watch her.The woman first bought a few small articles.After a little time,she chose one of the most expensive dresses in the shop and handed it to an assistant who wrapped it up for her as quickly as possible.Then the woman simply took the parcel and walked out of the shop without paying.When she was arrested,the detecitve found out that the shop assistant was her daughter.The girl `gav

答案

和“usual”做比较啊；因为人比平常少,所以比平常更容易监视一个人