The mortal sin was not the actual eating of meat on Friday, it was the disobedience of deliberately ignoring a Commandment of the Church that was the sin. The Church imposes certain Precepts upon the Faithful for the good of their souls. Unlike Divine Law they are imposed by the Church and as such they may be dispensed with by the Church.
After Vatican II the setting of these Precepts and their dispensation was put totally in the hands of local bishops' Conferences. That is when things began to unravel when Churches began to become more national than universal. Anyone who wants can ignore the bishops, they cannot force anyone to remain a Catholic.
People don't go to Confession mainly because they don't believe in sin or hell anymore probably due to the dearth of sound catechesis over the last half century.