Native UI components doesn’t support all the CSS stuffs like HTML.
If you check the code of react native’s slider plugin or even the SwiftlySlider are not the actual UISlider comes built-in with iOS. They both wrap set of views (UIView may be) and little animations to give a Slider like look and functionality.
It’s 100% possible to build a copy of react-native-slider in NativeScript, using similar logics. The question is who likes to write it? Could be possibly anyone who understands the framework, who actually needs it moreover who is not lazy
May be react native is around for a long time and has larger amount of plugins available. But I personally love NativeScript for it’s architecture, I don’t even have to write a plugin neither wait for one when I find something like SwiftlySlider / IndicatorSeekBar. I can directly import them into any NativeScript project and start using, it just requires little understanding about framework.