What keeps certain UK musical artists from crossing over to the U.S?

I've went down a rabbit hole of some UK artists with great music but are sort of obscure by the mainstream recently and wondered why they never ended up on the level of Adele, Ed Sheeran, Hozier etc. Some of the people I'm talking about are Foy Vance, Kaz Hawkins, Emeli Sande, Laura Mvula, Michael Kiwanuka and Jamie N. Commons. But wanted to know from a UK music perspective what the reason was. Is it terrible marketing and promotion by the record labels? Or the UK record labels only wanting to follow the music trends of U.S?