WebKit is the dominant engine because it's what powers Webviews on Android.
KitKat was released in 2013[1] as well as Blink in the same year[2].
Apart from Blink being a WebKit fork, WebKit itself is not "the dominant engine" anymore at least since 2014.
[0]: https://developer.chrome.com/multidevice/webview/overview
https://developer.chrome.com/multidevice/webview/overview Since 4.4 it is based on Chrome, not WebKit. Since I think version 6, on all the Google phones it defaults to using Chrome for WebView instead of the "WebView for Android" browser.