It's interesting to see how Freenode is the only large network that has seen substantial growth.

I can understand why. Most of the major API's and platforms have channels there, #facebook, #android, #github, and #jquery to name a few.

I would have expected gradual losses, but 60% in under 10 years is ridiculous

Such a shame, I was only introduced to IRC just over a year ago and loved it; spent ages studying how it works reading some of the RFC-1459 and learning the modes and commands. I'm surprised that more developers don't use it, it's a great way to communicate and discuss projects ideas and such.