When a store sells a game, EA (as it is its own publisher) recieves about 60% of that after taxes (not including platform games where they have to fork over sony and microsoft extra). Of that 60% it has to pay its employees and fund its projects (software, computers, audio as most studios have out-of-house audio). Note: modern games cost upwards of $30 million to make as well so there goes a stuff ton.
EA only gets money the first time a game is sold.
When Gamestop buys back your copy for a quarter of its original cost (ha!) and sells it for only $5 less than an original game, they are making about a 200% profit. EA sees none of that... no actually, EA sees less, as every copy bought that is used is a lost customer and thus a lost $60 to them.
I honostly do not blame EA for this.
All these issues will end once games go fully digital with things such as Steam.