While I don't agree WebSharper is monolithic - it's anything but that. I do agree that it is a bear trap. They could go bust at any moment and leave you with a big headache.
Even as a F# dev I have deliberately avoided using it because yes I agree with some of the sentiment here that the licensing model is a bit odd, but also the thought of needing to write a Binding for basically any JS library it doesn't support out of the box is quite a burden that will never go away. And can really slow down a new project that wants to iterate fast.
I firmly believe in using the best tools for the job at hand. So that means a F# back-end and a AngularJS front-end. It's a PITA maintaining two domain models in each, and similar validation logic etc, but such is life sometimes. What I lose in the domain model side, I gain back in a rich and vibrant set of available AngularJS modules and JS libraries.
It's a substantially nicer language than Javascript, and there's a lot of problem domains that are far easier solved in it.
People wouldn't use it because they don't want to learn Javascript. They'd use it because they don't want to use Javascript, on account of knowing better.