Let's look back to a couple of years ago. A friend of mine had 8 interview invites, attended 7 interviews and got 7 offers of admission. Let's say that the average spent for each interview trip was $500. So, that applicant spent $3500 on interviews and ended up declining 5 offers.
This year, with money tight and travel more expensive (or it was in the fall when fuel prices were so high), a comparable applicant might have received that first interview offer in October and dropped all further interviews, ending up with 2 interviews, 2 offers, $1,000 spent on interview expenses and 1 offer declined.
Now let's say I'm at a school that ordinarily makes 3 offers for every available seat knowing that more than half of the people with offers will not come here. With many great applicants having fewer offers on the table, some of the people who would have turned me down 2 years ago, won't turn me down this year when they have only 2 schools to choose from rather than 5. If I give out the same number of offers, I'm going to end up with too many students! So, if I'm deciding how any offers to make, I"m going to be conservative with the number of offers and be more likely to place people on the waitlist than in years past.
I think that may be happening but I have no hard information on which to base this scenario.