Leavers are pretty common in lower-mid keys, especially toward the start of a dungeon. Tank unga bunga pulls? Leaver. Tank pulls too slowly? Leaver. Someone doing relatively low damage on the first couple of pulls? Leaver. Someone repeatedly stands in bad and dies? Leaver. Someone says something snarky? Leaver. There is a multitude of reasons why people leave. The biggest being? True pugs (5 total randos) have zero social obligation/burden, so leaving has zero consequence. I've left Algethar Academy multiple times after it was clear the tree boss wasn't going to happen. Why waste your time? I do about 400 runs a season. I'd say an easy 10-15% of those have leavers.