It used to happen in previous FL game modes, but there was usually a reason. Dissension between players who actually wanted to win versus players who were only there for tomes was the most common cause (with the dominant voice winning). AFK players, Bots, and well known tome farmers would often get kicked on sight. The only other reason I ever encountered was when a semi-formed pre-made would boot a third wheel to open a spot on their team ... but that wasn't at all common, especially not at the end of a match. All of these things typically would happen fairly quickly at the start.