A supplement treadmill is a consentual relationship. Both parties must agree to this relationship in order for it to work. All the onus is not on the supplier end! As a consentual relationship, it must be, by definition, mutually beneficial. Those ending this relationship do so because circumstances have changed, and they no longer get enough benefit to justify maintaining this relationship.
Every designer is faced with choices all along. If they put everything a GM could need in the core book, that book becomes huge and too intimidating. If they keep the core book tight, they limit the game's applicability, scale, and/or scope. If they put out a bunch of supplements to cover the gaps, they are accused of facilitating the supplement treadmill. if they don't put out supplements, they are perceived as not supporting the game. If they revise a game, they are decried for changing things for the sake of change. If they don't put out a revision, they are vilified as old-fashioned and clunky. The list of Damned-If-You-Do-and-Damned-If-You-Don't choices goes on and on.
If a company puts out a lot of supplements, then people must be buying them, otherwise they would stop releasing stuff. If you don't want to buy these supplements, don't buy them. If enough people feel the way you do, then the treadmill will stop, because there really *is* no treadmill. The power to move that rolling walkway comes from your legs.