Derulo, 21, was due to work with the boys on their second album but the plans fell through as the US star was too busy.
Speaking to UK newspaper Daily Star, he said: 'Right now I'm trying to finish up my album so I wouldn't go and write a song for someone else. My focus is all on myself.
'I can't believe JLS are on their third album already. Things are much faster here than in America. People crank out albums one after another, which is awesome.
'I'm always open to collaborating but while my schedule allows me to do a lot it also deters a lot of things I want to do. I have to go with what's most important at that specific time.'