First, God gave mankind & animals only plants & fruit as food.
Gen. 1:29-30 “29 Then God said, “Behold, I have given you every plant yielding seed that is on the surface of all the earth, and every tree which has fruit yielding seed; it shall be food for you; 30 and to every beast of the earth and to every bird of the sky and to every thing that moves on the earth which has life, I have given every green plant for food”; and it was so.”
Although Abel tended sheep, we only see him using the sheep as a burnt offering to God. Nothing suggests they ate the sheep. Further, Noah is told in Gen. 6:21 to “Take every kind of food that you will need. Store it away. It will be food for you and for them [animals on the ark].” This indicates that the only acceptable food was still plant-based. God instructs Noah to bring 7 pairs of “clean” animals, which looking backward from Moses, seems to indicate clean for eating. But in just examining the text, the clean animals were used for a sacrifice immediately after exiting the ark. So it makes more sense & is in better keeping with Abel’s use of sheep, that at this point, clean animals were not for human consumption, but for sacrificing to God.
Immediately after the clean animal sacrifice from Noah, God clearly gives Noah & everyone after him every moving thing for food. God even goes so far as to add it to what He already gave them, “the green plants.”
Gen. 9:3-4 “3 Every moving thing that is alive shall be food for you; I give all to you, as I gave the green plant. 4 Only you shall not eat flesh with its life, that is, its blood.”
It’s important to note that He gives every moving thing. Not just clean. If it were just clean, He would have said just as He said pre-flood to bring 7 pairs of the clean & 1 pair of all others. He made a point to distinguish clean & unclean to Noah pre-flood; if it were intended in the food allowed, He would have said it here even more so.
Later, in Leviticus 10-11, God gives new laws that specify some animals as clean & edible and others as unclean & inedible. And the unclean animals can make unclean anyone or anything it even touches, except for a spring of flowing water. A small clue is given at the beginning of Lev. 10. God’s first words were that there are a lot of animals that live on the land. The more time had passed from Noah, the more animals had populated the earth, the more predator-prey activity, the more blood spilled, the more disease bred and passed among the animals. Perhaps this & the new wilderness conditions the Hebrews were then living in caused God to enact these new laws. Additionally, He gives other clues saying for the people to set themselves apart & be holy & clean like He is.
There are two beautiful parts to this. One is very practical. God is teaching them to be civilized & have good hygiene for their health. However, He is also teaching them about His nature: that He is holy and clean. He is using something so practical & physical in nature to demonstrate His God-attributes.
It was only at the time of Abel’s sacrifice that people began to worship God. By the time of Noah, ALL people except those on the ark were entirely wicked and godless. So by the time of Moses, we see God having chosen a people who were nothing and now He begins to train them up to teach them in very externally prescribed ways how to behave in their new community along with slowly teaching them who He is. Because at this point in time, God is very much unknown. There is very little history or prophecy as yet to show mankind who He is. He is yet a vague, widely unknown God, rarely sought after. So His use of external food laws to teach himself as holy is beautiful.
By the time we get to Acts, we see an entirely different world in place. The main parts of the world have become more orderly by governments. Cultures have been established where people have a sense of right & wrong (not necessarily Biblically so), instead of complete anarchy & wickedness & disorder as in Noah’s day. Similarly, instead of the baby people-group of Israel just coming out of captivity in Egypt under Moses, where they were suddenly on their own and unsure how or what to do, the cultures and society in Acts are older & established. Hundreds of years of prophecy, law, and history of God’s interaction with people are largely known and studied. Who God is is no longer vague. He’s painted a picture of Himself over time and history.
Jesus has come, died, and been buried & resurrected. From what I read in Scripture, a new covenant has been put into place. Here in Acts, the old food laws are suddenly displaced.