The Web Platform Is Too Low-Level
medium.com
medium.com
Frankly, if you can't replicate the native UI elements of the target platforms you intend people to develop on as a baseline, I don't know what you're doing. It's laziness, and to blame it on the premise that developers need to create their own look and feel, well guess what, you've just dropped the experience bar below native.
Default Ionic themed apps no longer look like native apps, they look like Ionic apps.
I believe that's what Google has been trying to solve with polymer and web components.
You still end up putting in the time, effort, and budget native developers will, so what's the gain?
Especially if you're a lone developer - it's one thing to learn the intricacies of one platform (like web), but learning the ecosystems for Android, iOS (maybe you don't even own a mac to develop with), and native desktop apps... it's just too much work for one person. But if you could just write it once and have a good experience on each platform, wouldn't that be amazing? I guess that's what React Native is trying to solve, too.