But they are not. They are merely a cultural respect for saints who are seen as a positive force in one's life. And the Lady of Guadalupe is venerated across Latin America.
I see no downside and, although I hesitate to speak for God, I suspect He accepts the offerings in the spirit they are meant.
God is not a prig.
The problem is, an offering to "Our Lady of Guadalupe" is not an offering to God.
I think the true saints, those who suffered for Christ, would be offended by prayers or offerings made to them rather than to Christ.
In the old testament, even God's angels were greatly disturbed when men bowed to them. They recalled how Satan tried to take God's place.
By making offerings to idols, you're doing no better than if you sacrifice a goat for zeus.
Exodus 20:4-6
4 “You shall not make for yourself a carved image, or any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth. 5 You shall not bow down to them or serve them, for I the LORD your God am a jealous God, visiting the iniquity of the fathers on the children to the third and the fourth generation of those who hate me, 6but showing steadfast love to thousands of those who love me and keep my commandments.
Exodus 34: 11”Observe what I command you this day. Behold, I will drive out before you the Amorites, the Canaanites, the Hittites, the Perizzites, the Hivites, and the Jebusites. 12 Take care, lest you make a covenant with the inhabitants of the land to which you go, lest it become a snare in your midst. 13You shall tear down their altars and break their pillars and cut down their Asherim 14(for you shall worship no other god, for the LORD, whose name is Jealous, is a jealous God), 15 lest you make a covenant with the inhabitants of the land, and when they whore after their gods and sacrifice to their gods and you are invited, you eat of his sacrifice, 16and you take of their daughters for your sons, and their daughters whore after their gods and make your sons whore after their gods.
17 “You shall not make for yourself any gods of cast metal.