From a 1999 interview with the members of The Police:  

Sting: People thrashing out three chords didn’t really interest us musically. Reggae was accepted in punk circles and musically more sophisticated, and we could play it, so we veered off in that direction. I mean let’s be honest here, “So Lonely” was unabashedly culled from “No Woman No Cry” by Bob Marley. Same chorus. What we invented was this thing of going back and forth between thrash punk and reggae. That was the little niche we created for ourselves.

Stewart Copeland: It was also the first time Sting said ‘screw the punk formula’. Sting started playing the song and I distinctly remember Andy and I making farting noises and going, ‘Yeah, right’. But then he got to that steaming chorus, we looked at each other and realised that maybe we should give it a try. In spite of our kerfuffling, Sting persevered and made us create something new.

Sting: The other nice thing about playing a reggae groove in the verses was that you could leave holes in the music. I needed those holes because, initially, I had a hard time singing and playing at the same time. So if we had a signature in the band it was…

Andy Summers: Big holes?