It's pretty simple, really. Just as with DRM, companies try things until they find something that works. The actual key is to hide your control method behind something people like, such as Steam DRM.
With the games themselves, the first solution was simply the market moving toward digital, which is obviously a huge boon. Even when a publisher is offering a digital game on sale, they're making far more than a used copy being sold, where they get zero.
The second piece has been the rise of DLC. At first, DLC was mostly throw-away attempts to make a little extra profit but developers have since realized that by offering DLC that people really want to play, they can make far more money. DLC has become an important part of the industry.
It's kind of emulating the car industry, where cars themselves have a modest margin compared to aftermarket sales.
