It's not just about revenue generation. I bet they are doing this to prevent Amazon from deploying a version of Akka as a service on AWS.
I think that makes this change worse, though: it means that the new license will infect many more projects--like Spark, for example. And they won't even be making security patches to existing versions available under the old license. "Nice project you got there, it'd sure be a shame if some unpatched security flaw came along and ruined it," they're saying.
edit: I wasn't aware, but Spark stopped using akka several years ago. But the basic point still stands.