Their songs are formulaic. I'm sure many of these 2 guys' songs are played in this video that cycles through a long list of hit songs which have the same progression (transposed into the same key so the similarities can more easily be noticed) https://www.youtube.com/watch?v=oOlDewpCfZQ
So perhaps anyone can write the songs, but not everyone has access to the pop stars (or access to these 2 guys).
I'm not an expert song writer myself, but I am a musician and lover of music. Based on the fact that there's awesome music noone's ever heard of or that doesn't get as much play as some lesser quality music, I have to echo the common sentiment that the music industry is a fashion show/popularity contest with gatekeepers (still). Not saying it's not all a sham, I think the difference that comes from the human performing is huge, and I love to see and hear that.