- It’s the easiest browser engine to use in an elementary application.
- It’s got modestly better integration into elementary OS.
- It works very well, and is getting better.
- Other elementary apps like Mail use it.
And it uses WebKit2 for significant security, performance, and web compatibility improvements.
Maybe these are weak arguments and a better case can be made for another engine (say, Servo), but they’re strong enough for Odysseus to keep using WebKit for the foreseeable future.