Why the A cycle Lectionary is used in Lent?
Historically the stories from the Gospel of John (the woman at the well, the man born blind, Lazarus) have been a part of adult preparation for baptism. The Gospel of Matthew’s account of the Temptations of Christ and the Transfiguration were also traditionally used for this preparation. Over the centuries Lent became used as the official time of preparation for adults who want to be baptized (i.e. the Scrutinies).
The themes of these Gospel readings (overcoming temptation, revelation of Christ, encountering Christ, gradual understanding of Christ, and receiving new life) are perfect for preparing for baptism and Easter.
If a parish has a Catechumenate that is undergoing the Scrutinies then Cycle A makes the most sense to be used during the Lenten Sundays no matter what the Yearly Cycle happens to be at that time. However, in years that are not already Cycle A, Cycles B and C may be used in their respective years if the parish does not anyone for baptism that year.