I think I've noted this here before, but 'Shape of You' is literally the most popular song in Antigua.
I suspect his popularity is tied up with a particular kind of Englishness that the Harry Potter books and films successfully sold to the world.
It's not a catchy tune. Craners girlfriend couldn't hum it and nor could I.
You try humming any of his songs. You won't be able to. The 'catchiness' is from his supposed lyrical skills, which also don't exist.