And how are you proposing to set up this manufacturing plant on the moon? This requires specialized parts, raw materials, etc shipped from the Earth. It's not like we can send some "moon colonists" over and have them get going. There are certainly raw materials on the moon, but it's not like the ones we need are going to be easily accessible.
Remember that the more exotic materials we use for space exploration are not easy to get, even on earth where we have the benefit of easily available oxygen/water/labor. Setting up mining, drilling, and excavation facilities on the moon is itself a massive undertaking with dubious benefits, unless we prepare with EXTENSIVE surveys that let us know exactly where the biggest concentrations of certain materials (mostly heavy metals and the more exotic semi-conductors/rare-earth metals) are located. If they're not concentrated in a small area, setting up multiple mining facilities to feed a single central manufacturing plant will be difficult. For the forseeable future, we're not going to be mining asteroids OR the moon. We're getting raw materials from the Earth because that's going to be the most cost effective for at least the next couple generations.
Think about it this way: try mining for iron in Michigan, for alkaline earth metals in Nevada, for copper in Montana, for Uranium in Tennessee, and then shipping it all to Iowa for processing and manufacturing. Sure, we can do it, but we spent decades getting the infrastructure in a rather human-friendly environment. And it still wasn't easy or cheap to set that up. Now try it in a hostile environment, like the moon.
Even the North America colonies of the 16-18th centuries required MASSIVE aid from their respective home nations in terms of new colonists, finished goods, and constant re-supply. And that's with the benefit of having relatively friendly weather, bountiful natural resources, and free water and oxygen. The US was built of colonists. It's massive industrial base was fed by a constant influx of colonists (i.e. cheap labor). You won't have that on the moon. The economics really don't work out.
The engineering challenge of setting up any sort of significant manufacturing plant on the moon is on the same order as setting up a manufacturing plant in orbit. But with the downside of having to constantly ship things from Earth to the Moon. It's be easier to launch them from Earth to LEO. That's assuming things aren't even less friendly to human life and manufacturing on the moon than we currently know.