Why Current flowing through a forward-biased junction dissipates power equal to roughly the forward voltage drop times the current, and that power turns into heat right at the tiny junction. If the heat cannot escape through the package and heat sink fast enough, the junction temperature climbs past its rated limit (commonly around 150 C for silicon) and the semiconductor material and its bonds are destroyed. So the current rating of a diode is really a thermal rating in disguise.
Watch out Excessive inverse voltage is a real diode failure mode, but that is reverse breakdown caused by exceeding the peak inverse voltage rating, not by too much forward current.
Too much current equals too much heat: diode current ratings are really heat ratings.