Well I think the biggest difference is purchasing power of the companies behind those other solutions in terms of marketing. Flutter has gotten this the most right, so far -- they make very published developer resources, and market aggressively, they have things like the Flutter Development Show[0], and little 30 second clips introducing parts of the platform[1] . It's a good thing (they're innovating in the documentation/dev experience space), but taken cynically it's just a marketing ploy.
I hate to say it, but lately people have been applying the same advertising and marketing logic they use on consumers on developers rather than necessarily making the best product they can and letting word spread organically. It's a bit of a chicken and egg problem -- you usually can only build the best product with help from others, which means getting in front of them, but usually you want to make a good thing so you can justify getting in front of the developers in the first place... So people put out shitty tools, then just iterate after the community shows up and finds out there are lots of rough edges (see: mongo, react, dart, etc).
The last I'll say on the subject is that "developer evangelists" are basically paid marketers/advertisers.
Nativescript also has this thing where it was popular years ago, but has recently seen a surge in popularity -- you have projects like nativescript-exit[2] (which provides a cross platform way to exit the app from JS) that have code from 2 years ago. This is actually a really great point for nativescript, because solidly written plugins like nativescript-exit really are solid -- I very recently used it in a project and it just worked. The integration points available in Nativescript have a very high potential (not to say other platforms don't).
[0]: https://www.youtube.com/playlist?list=PLOU2XLYxmsIK0r_D-zWcm...