Eight million is a lot, no doubt it must have been over time. My initial thoughts are that it's possible they were sacrificed, cult-like, to
Anubis. Or was that a Canidae cemetery, with not wanting to mix them felines. That which would also account for the high number of mummies. It
doesn't seem likely they were used to experiment with embalming techniques, as there would be more than just Canidae.
Human sacrifice in Ancient Egypt, as with animals, happened after a pharaoh died and they wanted the servants and companions to go to the afterlife
with that person. This practice didn't go beyond the First Dynasty. Why would they have their own cemetery then? That's why it seems for a
different, or general burial reason.
Here's a few clues from Wikipedia
Animal Mummy...
Animals buried in sperate tombs from people:
At the tomb KV 50 in the Valley of Kings, a mummified dog and baboon were discovered buried together, though the owner is unknown.[10]
Source:
en.wikipedia.org...
Religious Ancient Egyptian Cults:
Over time, religious cults emerged for the worship of each specific god. Two main types of worship distinguished the cults—the first choosing to
worship the god through mass mummified animal offerings and the second selecting a totem animal to represent the god,[4] which was mummified at the
time of its death.
en.wikipedia.org...
Religious Offerings:
Before animal mummification became common, these offerings were usually bronze statues depicting the animals.[9] However, eventually a cheaper
alternative to bronze statues—animal mummies—became the most popular form of offering. Literally millions of these mummified animals have been
discovered throughout Egypt. Inspection of these mummies, usually done through CT scans which allow researchers to examine the skeletons of the
mummies without damaging the outer wrappings, has suggested that these types of animals were bred for the sole purpose of offerings.
en.wikipedia.org...
Nineteen Tons of cat mummies shipped as fertilizer:
Cats were mummified as religious offerings in enormous quantities and were believed to represent the war goddess Bastet. This cult was primarily
centered at Thebes and Beni Hasan beginning in the Ptolemaic Period. At Beni Hasan, there were so many cat mummies that at the end of the 19th
century, a total of 19 tons of mummified Egyptian cats were shipped to England to be used as fertilize
Also from:
en.wikipedia.org...
So, there you go... possible millions of cats mummies found, but used for gardens...