That's only some "core" for the software, not the full software, which is kept proprietary.

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 wouldn't say about what available on GitHub today, but up until year ago all source code was included and they only sold precompiled binaries and support. Also I doubt they can really change anything about that because Synergy never required CLA and it's under GPLv2.

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.

Isn't that more proof that it doesn't work well though?

Why would they do all these changes if the previous model worked well for making them money?

Previous model was usual open source community-driven project with donations and it's obviously didn't worked, but Synergy was developed by different team at different times and looks like they find what works for them. It's tarted 3 years ago:

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.