Its not just the 15mil though, its the perception that the cards had or have value on the secondary market, or no value at all (proxies, not allowed in tournaments). And they can print power 9 proxies now whenever they want, and if they want they can pile them up and burn it all on a pyre as you say... essentially saying that the cards are in fact worthless.
Not to mention, when they break the spirit of the reserve list, they break the goodwill of the community at large. The community made their opinion known on this matter. I am not part of the mtg community anymore since I don't play anymore, but they have spoken with their wallets in a pretty significant way. The sets failure represents not just loss of revenue, but loss of value for the cards in general if they continue this practice in the future.
The entire reason mtg has lasted as the #1 card game for so long is because of the perceived value of the cards, leveraged against the cards utility and use in tournament legal play. Except the creator of the game has stated himself that treating mtg as a collectible is actually bad for the mtg community. This entire idea of artificial scarcity is coming back to bite them.
"If you are treating it [mtg] as a collectible first then you aren't doing your players any favors" - Richard Garfield