The main problem with assembling them is that there are a lot of blocking processes. Every time a single part is on backorder, the entire production suffers from this. Even with a small legion of people building these, it takes a few manhours to build a machine.
Outsourcing this is not a very good idea, as it would take quite long for the builders to be on a somewhat desirable speed and the other party needs to be big enough to cut out overhead (which is the main problem). Sending 10 packages to a single builder just doesn't cut it as the administration of 20 ish of such builders would be a complete nightmare (and therefore freakishly expensive). Quality control would become a major issue all of the sudden.