Many/most airlines preserved status, rolled over qualifying miles/trips, and were quite good with retaining certificates etc the past three years. I kept my delta diamond status even though 2020 changed my travel from 2-4 international trips per year to 0-1. Apply that across the entire population of status holders and the number of concurrent status holders will increase.

In addition airlines have moved a TON of revenue from pure business travel tickets to “premium” seats and “non ticket” revenue like small upgrades and cobranding cards. These again feed in to the numbers of travelers getting status and using amenities like lounges.