Actually, it's who controls the server, not the key. The reason they're called game key cards if because they're literally a key. You own the key.

The issue is, they own the servers, and again, once those are down, you can't download the game anymore. The card is just used to download the game tho, and verify that digital copy is valid with your key, so whoever lasts uses it once they go down are the final owners of the digital game. Unlike a physical game, where it doesn't matter if the company itself goes bankrupt.

Like I said, they're a step up in that they're this weird hybrid of the standard digital game front and a physical item you can at least lend and sell for some time. But they're not as good as a physical copy or a drm free digital copy.