The detailed history of Yahwist cult is largely lost to us. We have only the work of narrowly focused compilers and editors to draw from in the OT and archaeological insights from such a distant past are sadly sporadic. Just how did the concept of death develope and at what point did the veneration/consultation of the dead become anathema to Yahwism? There are many evidences in the OT that the people in general clung to their past practices of necromancy and invocations despite the efforts of Yahwist reformers of the 7th-5th centuries.
An interesting evidence that the Yahwists themselves retained the early practice of offering food for the dead is the presence of of bowls and vessels in assumed "Israelite" tombs in keeping with general Palestinian practice. Some have speculated that the bowls must have been for feeding the mourners in the Israelite cases but this defies the obvious.
A verse that may demonstrate that this practice of gifting food to the dead was acceptable practice is Deut 26:12-14:
12 When you have finished setting aside a tenth of all your produce in the third year, the year of the tithe, you shall give it to the Levite, the alien, the fatherless and the widow, so that they may eat in your towns and be satisfied. 13 Then say to the LORD your God: "I have removed from my house the sacred portion and have given it to the Levite, the alien, the fatherless and the widow, according to all you commanded. I have not turned aside from your commands nor have I forgotten any of them. 14 I have not eaten any of the sacred portion while I was in mourning, nor have I removed any of it while I was unclean, nor have I offered any of it to the dead. I have obeyed the LORD my God; I have done everything you commanded me.
At first it may be that the Deuteronomist was condemning the practice of offering food to the dead but upon closer examination we see that the issue is the ceremonial cleaness of the tithes gifted to the priests. IOW the practice itself is not condemned but simply that no part of the foods used as tithes should be handled when "unclean" (eg.having menstrual discharge or when touching a dead body).
Even later in the 3rd century BC book of Tobit (4:17) the practice is to be encouraged: "17: Place your bread on the grave of the righteous, but give none to sinners."
Apparently the ancient practice that clearly manifest a reverence for the dead had lost is offensiveness to the Yahwists through years of fighting a losing battle.