its also a transaction that a native game sellign service can setup to allow for a cut of profit if trade is done on the site, which could give devs a tiny bit more money. if the threat of additional aftermarket sales didnt threat when its physical, then why did devs make physical versions of the game. Theres always some room to debate what ifs, but it doesnt stop the fact that resell of physical did not stop devs from wanting to sell physical, and you can't automatically apply it to digital immediately either.

a e-tailer can choose to create an easy to buy system and then charge some % of the selling fee ala gamestop, and choose to also redistribute some of that fee to the dev if the platform wanted to get on the devs good side after obliging to said law. a lot of things can happen and its not wise to automatically assume the worst outcome.