It's much more than a lack of positive evidence for a historical Moses, but a great deal of archaeological evidence against the Biblical narrative of Israelites ever being enslaved in Egypt, against any Exodus event or sojourn or presence of a large population (or even a small population) in the Sinai at the relevant time and against any conquest of Canaan or influx of population into Canaan.

A good book on this is The Bible Unearthed by Israel Finkelstein and Neil Asher Silberman, but William Dever gives a good presentation here, which more or less gives the mainstream view of ANE archaeologists.

There are some theories that do not exclude the possibility of some historical memory being present in the mythology, i.e. much smaller scale escapes or migrations of Canaanites from Egypt (though no evidence for specifically Israelites has ever been found in Egypt and the archeology seems to show them beginning to arise from native Canaanite populations only around the 13th Century) or Moses as a personification of a (possibly Midianite) priesthood or Yahweh cult, but virtually no secular historians believe in a literal Moses or Exodus anymore.