As compared to other ancient civilizations?
A number of factors here.
Number 1) like many other ancient civilizations, they had a very strong funerary practice - meaning they buried objects on purpose. Things will more likely be preserved of put there on purpose, rather than just objects discarded.
Number 2) the amount of effort they put into these elaborate funerary practices - the city of the dead, thousands of mastabas, massive layered mastabas (aka pyramids) this means that simply the quantity and quality of thing deliberately placed in preservative states is just staggering. There are some historians that go so far as to say that the collapse of ancient egypt was because so much of their economic output (in terms of labor and material resources) were devoted to non-econmoc productive acts (ie the dead) that it just wasn't sustainable.
somewhat obvious: in light of the above, they were really really really into preservation. Mummies. As well as persevering everything else they buried. They were good at it.
egypt is very dry desert climate. It's only able to be a locale of great ancient civilizations because of the unique nature of the nile. This climate is very very good for preservation. Other civilizations were in more erosive climates (moisture, freeze thaw cycles, animal life)
that dessert climate also has a lot of sand, which shifts more easily than other soil types. This buries things faster, preserving things faster (as well as obscuring things from raiders)