The Catholic Catechism is a teaching tool about the Catholic faith. The Teaching Magisterium of the Church could have chosen another sequence for the seven sacraments, but it stayed with the most common and traditional way of listing the sacramennts.
Why this sequencing of the sacraments?
The first three sacraments mentioned are those involved in Christian initiation.
According to the Catechism of the Catholic Church, “the sacraments of Christian initiation — baptism, confirmation and the Eucharist — lay the foundations of every Christian life. ... The faithful are born anew by baptism, strengthened by the Sacrament of Confirmation, and receive in the Eucharist the food of eternal life” (No. 1212). The Catechism goes on to say that, “The holy Eucharist completes our Christian initiation” (No. 1322). - Restored order for sacraments a growing trend
Baptism, penance and the anointing of the sick are sometimes referred to as the
sacraments of the dead and as such are at the faithful's disposition when in need. Since we should be in the state of grace before getting married or upon being ordained as a priest these sacraments are placed next in the list.
Those sacraments which can be validly and fruitfully received when a person is not in the state of grace. They are baptism, penance, and, if needed, anointing of the sick. These sacraments confer or restore sanctifying grace and confer actual graces when received by one who is already in God's friendship. - Sacraments of the Dead
Most of the faithful will eventually choose marriage over Holy Orders and thus marriage is normally listed as the sixth sacrament and Holy Orders as the seventh.
Many Catholics do have a different sequence for the seven sacraments of the Church, such as the following:
The Seven Sacraments of the Catholic Church
II. Reconciliation (Confession)
III. Eucharist (Communion)
VI. Holy Orders
VII. Anointing of the Sick (Extreme Unction)