More than half of the 25 largest games on Facebook lost users in April, but the trend picked up last month.

Is the Facebook platform collapsing? That’s not what the data is showing. Social game developers of all sizes continue to see growth (check out our weekly top 20 lists for more on that).

Why, then, are so many of the largest games losing so many users? One reason could just be age. Almost all of these apps were launched last year. Game lifespan varies depending on genre, quality, the number of updates, and other factors — and some of these titles, like Restaurant City and Farm Town, are more than a year old.

But another factor is obviously Facebook’s removal of notifications at the beginning of March. That channel was a key way that most games grew and maintained user engagement last year. Facebook removed the channel because so many developers used it so aggressively that it became filled with spam. With each change in user communication, developers have to adapt their game design – but it’s often hard to prevent at least some period of traffic loss.

What’s left for developers? Organic growth through news feeds, email and the soon-to-change requests features — and advertising and cross-promotion.

These channels provide slower growth, but are also harder to spam; send too many emails to a user about a game and they’ll filter out the sender.

> Continue reading on Inside Social Games.