How is an infant properly disposed, cognitively, to received these graces, but an adult is not. If an infant’s parents promise to raise the child with Catholic teaching as a condition of receiving baptism, why couldn’t an adult’s promise to do the same thing for themselves be sufficient to receive the same graces.
Additionally, regarding salvation via Baptism of desire: I haven’t looked into this much, but my initial take on the concept lead me to wonder the following. Aren’t the graces of baptism what we need for salvation? If these same saving graces are received by desiring baptism, then would my children receive the graces of Confirmation through earnest desire, as well. If so, then why participate in a specific rite to receive what’s already present?
Catechism
1231 Where infant Baptism has become the form in which this sacrament is usually celebrated, it has become a single act encapsulating the preparatory stages of Christian initiation in a very abridged way. By its very nature infant Baptism requires a post-baptismal catechumenate. Not only is there a need for instruction after Baptism, but also for the necessary flowering of baptismal grace in personal growth. the catechism has its proper place here.
1234 The meaning and grace of the sacrament of Baptism are clearly seen in the rites of its celebration. By following the gestures and words of this celebration with attentive participation, the faithful are initiated into the riches this sacrament signifies and actually brings about in each newly baptized person.
1258 The Church has always held the firm conviction that those who suffer death for the sake of the faith without having received Baptism are baptized by their death for and with Christ. This Baptism of blood, like the desire for Baptism, brings about the fruits of Baptism without being a sacrament.
1259 For catechumens who die before their Baptism, their explicit desire to receive it, together with repentance for their sins, and charity, assures them the salvation that they were not able to receive through the sacrament.
1260 "Since Christ died for all, and since all men are in fact called to one and the same destiny, which is divine, we must hold that the Holy Spirit offers to all the possibility of being made partakers, in a way known to God, of the Paschal mystery."63 Every man who is ignorant of the Gospel of Christ and of his Church, but seeks the truth and does the will of God in accordance with his understanding of it, can be saved. It may be supposed that such persons would have desired Baptism explicitly if they had known its necessity.