Phonegap, Cordova or other similar tools allow developers to write HTML and CSS, and employ the mobile's native API's.
The app is a wrapper, which loads html from a webserver.
Developed for Apple's ecosystem (iOS, macOS). Swift is a young and modern language.
Included devtools like Hot Reload make it very developer friendly compared to java or objective-c.
Objective-C is the core language for iOS development. Its relatively low-level, which Apple solved by creating a more accessible language: Swift.