Why Are Some People On Dating Sites For Years?

I tried dating sites two years ago-and tried again recently-one thing I have noticed is a lot of girls I seen on dating sites two years ago are still on the same sites and other dating sites two years later-one girl for example she has two usernames on various sites-supergirlforever and twilightgirl- in her profile she states all she wants is a long loving relationship-after two years on various sites wouldn,t you think she would of found that by now with a guy-do you think its a kinda red flag when the same people are on various dating sites for years?