Hindquarters of a cow are not kosher, so brisket is a cut of beef that Ashkenazi Jews have made and enjoyed for many decades. It's a tougher cut of meat, therefore it used to be cheaper, and can be made tender and delicious when cooked over long periods. It used to be served at Passover because it was the frugal choice that could feed a crowd, but it's now also an ongoing tradition.