I'll try this a few times, why not? I'm a standard player who cracks packs I win at my LGS, and do a few prereleases, but I don't buy packs otherwise. I buy playsets (or fill them out with singles if I get lucky pulls) for the standard brew I want to play.
Most players like me who are playing on a reasonably affordable monthly budget who get a single, high-$ mythic from one of their few packs sell it off to get the card(s) they want for their brew; and, in so doing, lose a lot of the value - or 'feelgood' from that lucky pull. As I figure I'm only getting half the value from a lucky pull I don't need and end up selling, I am less incentivized to buy more packs.
Buying more packs is what makes wizards $.
Now with
Brawl, a player like me that got a Chandra or scarab god in a lucky pull and is not interested in building a deck with a full playset may not sell it for half-value but rather keep it for a
Brawl Brew Idea. All of a sudden, lucky pulls from packs have double the value and I am doubly incentivized to buy another pack...or five.
This works the same way for
Arena economy, btw. I can't see WotC
not doing this to help bring in some edh players without having to debug all the interactions with old cards, as well as increasing the perceived value of random digital cards players get in
Arena but don't fit in the constructed standard
arena deck they want to play.