I don't see anything 'wrong' with GWT, just as there is nothing inherently wrong with writing iOS apps using Ruby (http://www.rubymotion.com/).
For example the Inbox team did a fantastic job re bringing a great user experience to multiple platforms and I guess they were glad that they could use one language throughout instead of having to jump between various tools and idioms (see http://gmailblog.blogspot.com/2014/11/going-under-hood-of-in...).
It's just that like you mentioned people do have different preferences when it comes to languages/tools/ecosystems. That's all.
There are people building web services using PHP, Ruby, Python, Java, Haskell, Elixir, Erlang, Go, C++, JavaScript, Dart. Why not also have this choice on mobile?
For example the Inbox team did a fantastic job re bringing a great user experience to multiple platforms and I guess they were glad that they could use one language throughout instead of having to jump between various tools and idioms (see http://gmailblog.blogspot.com/2014/11/going-under-hood-of-in...).
It's just that like you mentioned people do have different preferences when it comes to languages/tools/ecosystems. That's all.
There are people building web services using PHP, Ruby, Python, Java, Haskell, Elixir, Erlang, Go, C++, JavaScript, Dart. Why not also have this choice on mobile?