More classic sound to songs (piano, acoustic guitar etc) less electronic or current trends which American boybands follow making European boyband sounds stay fresh and long lasting.
European boybands/members don't have to be as clean cut as American member counterparts and can still have huge careers even with drug/sex scandals due to wider demographic audience
European boybands generally are less driven by 'World domination' compared to their American counterparts though still sell just as many records just not in the US itself.