The parents bring the child for this first Sacrament of Initiation, and it is THEY who pledge to raise the child in the faith. At Confirmation, the child, now older, chooses freely to accept the final Sacrament of Initiation, and become an adult in the faith.
Just because a person is a single mom doesn’t mean they won’t raise the child in the faith. The odds are better that they will if they request baptism for their child and can go ahead with it.
Just personally, I had a co-worker whose parents were not allowed to get her baptized in the Catholic Church for some reason. She and her parents had a life-long bitterness against the Church and she became a Buddhist as an adult. She now has children, being raised Buddhist. So, the refusal to baptize has so far caused three generations to shun Jesus, and who knows how many will follow?
There are no guarantees that the mom will not abandon the faith or live in sin after the baptism, but there are no guarantees for the rest of us sinners, either.