I’ve never seen anyone play serialized cards in competitive Magic, and I’m not convinced that the really hardcore competitive players would even consider buying any. Most competitive players. Only buy the singles they need rather than large quantities of cards, so I don’t think there’s been any drop from that crowd.

However, you may be correct about the marginally attached players overspending. Those that will play a tournament if it’s convenient but never grind or travel for them. Those types could well have spent themselves out and so the bulk of players is lower than it used to be. On the other hand, there may just be fewer results overall to report in the first place.