The most common motors used for modern drones are brushless outrunner motors and I have heard that they are simpler to manufacture and are less susceptible to issues when being mass-produced than brushed motors because the only parts of the brushless outrunner that rub together are in the bearings (they don't require a brush to be at just the right spot or pressure or anything). If this is the case, why do brushless motors tend to be more expensive than brushed motors?
Brushless motors are typically CNC machined for a large part of their manufacturing process. The top part of the bell and bearing race are machined from aluminum. The shafts typically steel or a titanium alloy and are CNC machined in a lathe. The steel flux ring is typically pressed, and the stators are stamped from existing templates for the most part. The machining is somewhat expensive comparatively, the stamped and pressed parts are relatively inexpensive compared to the other costs involved. In general, it's a fairly complex manufacturing process, and the materials are not necessarily the cheapest. The cost goes down as volume goes up, and a lot of what we use in the DIY drone industry is fairly small batch production, which helps drive up the cost. There's also the supply and demand question and to a certain extent, the cost is set by what the market is willing to pay. That being said I personally know a lot of brushless manufacturers, and the race to the bottom on prices that we're seeing in certain parts of the hobby (low-cost FPV motors) are pushing the absolute limits of the margins.
Brushed motors, on the other hand, have essentially no CNC'd parts, almost everything is pressed or stamped including the can. Average quality brushed motors with average tolerances and efficiency are cheap and easy to produce. The cost with brushed motors comes when you need to increase precision, performance, and efficiency. However the advent of reasonably priced brushless motors has pretty much nullified that market, so all we're left with us the first category except in very narrow niche applications, none of which I've had the occasion to explore yet.