Some authors are more popular, sometimes a little detail in the fic hits many people's buttons and the basically similar fics don't have it, and sometimes people just have different taste than you. There are even some fics of my own that have a number of kudos that I personally don't think they deserve more than other fics of my own in the same fandom/pairing. It all comes down to people being different, basically, and arbitrary things like more people randomly happening to be online at a certain time on a certain day for reasons you couldn't guess.