Harvest is where first contact (or at least one of the VERY early contacts) occurred between the UEG and Covenant it is in the Epsilon Indi system.

Epsilon Indi is ~12 light years away from Earth.

In the 27 years of the Human-Covenant War the Covenant never actually found Earth. They just found a map to the Ark and part of the path happened to coincidentally to be on Earth. If that particular bit had been practically anywhere else they wouldn't have found Earth.

There is around 12 stars within a 10 LY sphere centered on Earth. Epsilon Indi probably isn't going to have orders of magnitude more than that.

Even ignoring the radio waves Earth would be emitting and the fact that any decent astronomical survey from Harvest would show that Sol is a perfect system to support life. Any sensible blind search pattern would have checked the closed star systems to first contact for human life.

The Covenant should have even been able to figure out that the UNSC has shit slipspace tech at that point so wouldn't be able to control a large far flung empire.

All they needed to do is check one solar system per month and they would have finished this war in like two or three years.

But NOPE, the Covenant can't find shit unless you give it to them on a map.