Why does the Catholic Church have different rites, and what are the differences between them, in a general sense, not the in depth particulars as that may take more than a few sentences in a reply. :-)
The best way to say it is that it comes down to practice in worship versus belief. The dogmas of faith are the same but the way the Mass (or Divine Liturgy in the Eastern Rite) is said varies. Pope John Paul II referred to the eastern and western rites of the Church as allowing the Catholic Church to “breath with both lungs”.