I think they mean the size of individual classes, so they're paying for more sections/instructors/instruction time in the ranking-relevant periods.
Though shrinking the admit size is another well worn tactic, as it's the easiest way to increase how "selective" you are which is another major ranking element, plus it helps you more cheaply achieve smaller average class sizes, though of course you're forgoing some revenue to get there.
Apparently there’s a common application thing now where you can apply to large numbers of schools for undergrad without spending large amounts of money.
The common application just means you don't have to fill out unique admission forms for every school. You still pay an application fee to every school.
In some other countries there's a national system with a single modest fee. In the UK this is 'UCAS'[1], a nonprofit org. You apply once, and indicate your top N (say, 5) favorite school+program. The applications are sent to the schools, and they can make you an offer.
If not accepted for any of them, there's a follow-up matchmaking service (called 'clearing' in the UK) to help find an unallocated spot.
From the common application site: While some colleges may charge an application fee, others have no fee to apply. And, many will offer fee waivers under certain circumstances, including financial need, veteran status, and more.
Based on a conversation with my nephew who applied to a double-digit number of colleges this past year, the application fees are apparently more the exception than the rule these days.
You can if you admit on objective metrics. If you only take people who are 215 pounds or above, you can fairly claim to reject everyone lighter than that, regardless of whether they apply.
