I think the problem isn't being able to resell games. It's the fact that it became "industrialized" reselling. Gamestop grew so big, and incentivized used sales

I think the problem isn't being able to resell games. It's the fact that it became "industrialized" reselling. Gamestop grew so big, and incentivized used sales so much (so much that on release day, unopened new copies of the game were opened by employees to sell as used for $5 less), that the sheer volume caught every game publisher off-guard. Used games stores have been a thing much before it became a problem (I remember selling games at EB Games). But because of Gamestop's growth and their aggressive pursuit of making sure their customers only dabble in the used games section, it became a serious issue. The 7-9 resales by Gamestop might not translate to 7-9x extra sales, but I would bet it is at least 2x. I know a lot of people that stopped buying their games new, but wouldn't buy them used unless they were from Gamestop (so basically no grey market, e.g. ebay or craigslist), because it was more convenient. In some cities, Gamestop had some many stores, that they had to compete between themselves.