Here's why:

* Order is a higher taxonomic rank than genus.

* A genus is a group of closely related species.

* An order contains multiple families, each of which contains multiple genera.

Think of it like this:

* Order: A large library with many sections

* Family: A section in the library

* Genus: A bookshelf within a section

* Species: A book on a bookshelf

Since an order encompasses multiple families, genera, and species, it naturally has more organisms than a single genus.