And even that could hurt their business if somebody used the core to build their own app for the same target market on top of it.
I pretty sure their "core" naming is just another way to promote usage of paid version, but you can still compile it yourself and easily remove all license checks.
Why would they do all these changes if the previous model worked well for making them money?
https://www.reddit.com/r/linux/comments/2fydpm/synergy_gpl_i...
Of course it's not shiny VC funded company with 10000% growth, but I guess it's profitable business. Though it's not that much different from what Red Hat doing by selling support even if it's on small scale.
Heck, they couldn't even put it on the iOS App Store for free...