@ccatron: because in more liturgical churches, the church year is a metaphor for life, and there’s a special part of each year set aside for celebrating each important aspect of human life and Christ’s life. It’s not that we can’t give up something for any random 40 days; it’s more like, this is the time of year where we think about this, and remember this, and in keeping with that, this is an important spiritual exercise.
Two of the important principles in teaching are that you master one thing at a time and that you come back to review things you’ve already mastered. In theory, you focus on the nativity every day, you focus on the Holy Spirit every day, you focus on the resurrection every day, you focus on forgiveness every day, you focus on penitence every day, and so on.
In practice, liturgical churches set aside a period of the year to especially focus on penitence, a period of the year to especially focus on the resurrection, a period of the year to especially focus on the nativity, a period of the year to especially focus on the Holy Spirit, and so on. In this way, because we’re focusing on one thing at a time, we get better at that thing; and because we come back to it every year, we get better at it over time as well.
This approach may not work for everyone—it sounds like it wouldn’t work for you—but there are many paths to Jesus. As long as the one you’re on works for you, I’m OK with it.