I've seen it happen so many times I can barely count. Groups that achieve very good results on the first or second try, and then just DISBAND for no reason.

Like, yesterday I had a group go on A12 and get the boss at 17%, only to have both tanks and a healer leave afterwards. Then, another got it to 40% on the first try, then 75, then 25, then 4 (FOUR!!!) and then disbanded. Only to have the next group have a much worse performance than the one that broke apart.

I've also seen similar situations on previous patches, on fights like Niddhog, A4, and even stuff from the previous expansion. What IS with this people? Why quit a group with a steady progression, get a 30-min timeout and then queue up again for a WORSE group?