See question above: Still, why is Selichot different than the Tefilos during the rest of the year?

Binyan Shlomo (Hacohen 36) further explains that there is a difference between mitzvos that apply to an individual and they are not part or represent the Avoda, we indeed tell him “Hamaschil Bemitzva Omrim Lo Gemor, “If one starts to perform a Mitzvah, we say to him, ‘carry it out to the end.’ However, mitzvos that are carried out by many together, as Tefila is, should be given to the many. Selichos, he adds, is different, because it may be difficult to find someone who is willing to recite them, as they are unusual, so compensation was instituted. He further debates if the above applies only to the one that accepted to lead the Selichos during the whole period.