Until last year, the Reserve and Platinum provided MQM boosts, which added to MM balance.

Edit: I would be shocked if there were more than single-digit hundreds of people who had accumulated more than 750k MQM by that route; in any event, these folks nearly by definition don't fly much.

(There also was a period, multiple decades ago, when card RDM counted for MM, but few from that period are flying now).