Some people aren't going to like this at all. "The Tyranny of Emotion" (Mic'd Up, January 29, 2016) includes a discussion with Michael Hichborn of the Lepanto Institute about the Alpha program being implemented in many places and notably in Detroit; and Dr. Jay Boyd, who offers an in-depth discussion of Sherry Waddell's Forming Intentional Disciples with some cautions.
The upshot seems concisely expressed in the question: why are Catholics embracing these 'watered-down' and 'protestantized' sorts of programs when excellent Catholic alternatives exist, such as Servant of God, Fr. John Hardon's Marian Catechist Apostolate, now under the sponsorship of Cardinal Burke? Not to mention all the hazards of emotionally-charged low-information evangelization with potentially misleading components. Food for thought. One can hardly say "food for feeling," can we!
Update: William J. Cork, D.Min., "Is ALPHA for Catholics??," offers a fairly detailed outline and critique of Alpha, arguing that it promotes (a) an individualistic Christianity, (b) a congregationalist ecclesiology, (c) an evangelical perspective on the sacraments, as well as (d) a charismatic agenda. The author concludes:
Despite the commendable intent of Alpha to evangelize the unchurched by facilitating an initial encounter with Jesus Christ, we must conclude that even with a Catholic supplement, it remains deficient, and cannot be recommended for Catholic use. Alpha does not fulfill the expectations for Catholic catechesis and evangelization, and presents what Catholics must see as an impoverished and distorted Gospel. It is not "basic Christianity," but is Charismatic Protestantism. To tack Catholic elements to be tacked onto the end, especially issues of Church and Sacrament, denies the integral nature of Christian revelation.