Because the same book of Hebrews says that animal sacrifices have ended once for all. And wouldnt you think the writer of Hebrews was familiar with Ezekiel 40-48? One would think that if future animals sacrifices were still a possibility that there would be some hint of it in Hebrews or somewhere else in the NT. But there is not. We see the opposite being taught quite forcefully. In fact you can search long and hard in the NT for any hint of all the futurists millennial imaginations and you will not find them.
Obviously the NT writers did not interpret the OT prophecies as the futurists do.
“Because the same book of Hebrews says that animal sacrifices have ended once for all.”
The writers were talking about the sacrifice for sin had ceased, not memorial. By the way, when did the sacrifices for sin under the old covenant cease, when Jesus died or when the temple was destroyed in 70 A.D.?
The “clouds” mentioned in Daniel 7 are masculine gender and Daniel says “with” the clouds of heaven. Matthew uses the feminine gender for clouds and says “coming in the clouds of heaven”. The Hebrews reference to surrounded by “clouds” of witness is the neuter gender. The feminine “clouds” is the Old Testament cloud that led Israel.
You still haven’t answered the question, were the two covenants overlapping for forty years?