I spent years of my life on the problem of generating useful multi-platform code from a GUI tool and integrating it into designer and developer workflows. Before giving up I made React Studio (https://reactstudio.com) which is owned by my co-founders now.
It's insanely difficult. Nobody's needs are exactly the same, and nobody can agree even on the basics of how a web app is structured: where does CSS go, how do you update your global data, etc.
The abstractions I had to build to handle that then increased the learning curve to such levels that it became more like a CAD tool where you'd practically need to train teams into a new way of thinking for them to become productive. Having traction with a few customers never seemed to translate into something scalable. (Maybe with an actual sales team an enterprise strategy could have worked.)
My original version of the product was a mobile-only UI tool that generated native code for iOS and Android. In retrospect that was a better product than trying to expand into full-blown web apps. In native, a button is a button and a tab bar is a tab bar (with small differences between UIKit and Android); in web anything can be anything, and it's a point of pride to reinvent the basics constantly, so a tool must somehow adapt to the shifting tides of how CSS must look this year.