These things are made in (I assume) the stereotypical "Chinese sweatshops" and the employees get VERY low wages. That cuts down on the vast majority of the price that goes into manufacturing these items.
Aside that Chinese wages are no longer that low, the costs of your ebay "bargain" are low because the components are pretty much bottom-of-the-barrel stuff that is cheap, and the design is a copy of something that's already available.
I'm sure the total price of the components in an AWG is not $500 worth
Considering that some of the decent entry level AWGs don't even cost $500 in store there certainly are cases that this is true (it certainly isn't for better AWGs like the Keysight 33500/33600 Series). But the price of an item is not solely detemined by the physical components that go into it. The firmware needs to be developed, and good developers don't work free. The hardware also needs to be designed, again by people that don't work for free. The design needs to be tested, manufacturing needs to be setup, the support infrastructure needs to be setup, and so on.
Plus there's the research that goes into stuff like Keysights Trueform technology which needs to be paid somehow.
, and that the high price of most of these brand-name devices comes from the labor used to make them (in the "parts and labor" calculation of the price). Items made entirely in China (because of their very low wages) cost only a tiny fraction of those that are either made entirely outside of China, or items that are made mostly outside of China (but with a few parts being made in China).
Noname Chinese stuff is cheap because its generally a copy of some very basic existing hardware design, produced by the cheapest components you can find, with either hacked together or cloned firmware.
A product that is sold is priced according to 3 factors. These are parts, labor, and profit. Lets say the price of all the parts in an AWG is $50, and the price that it costs employees to make it (at a reasonable wage) is $500, and the company is trying to make a $100 profit on each item. They will sell it for $650 ($50+$500+$100). But now in China, they probably are going to only charge the employees $10 for each device manufactured, and be willing to be content with a lower profit, of maybe only $10 per unit. That means that for a similar product made in China it's going to be sold for only $70 ($50+$10+$10). That's why I think stuff made in China is so cheap.
As someone who runs a business with enclosed production for a living I can tell you that your imagination has little resemblence with reality. For a start, there are a lot more factors playing into the price of a product, some of them I already listed above. Then there's market consideration (i.e. what is the specific market willing to bear), projections of the through-life support costs required, and lots of other parameters that make up a product.
You may believe that the Chinese have somehow found the panacea of manufacturing, but they haven't. They managed to produce cheap because human labor was seen as consumables with no regard for worker health or safety, by stealing IP developed by Western industry, ignoring basic product safety standards and other practices that in other countries would be considered fraudulent. China isn't the only one, though, Japan, these days considered a source of high quality/high precision equipment, went through a similar phase, and like Japan China shows more and more signs that at they want to move away from being the global source of cheap crap. Rigol and Siglent are early examples of Chinese industry starting to find its own way and develop their own products, but that also means their stuff is now more expensive than the unlabelled crap you seem to be so fond of.
And by the way, what do you consider to be reasonable frequency accuracy, if 10ppm isn't? And what do you consider to be reasonable sample memory, if 2048samples for a waveform isn't reasonable?
For a somewhat decent low end AWG I'd look expect better than 2ppm (which even the cheap Siglent AWGs are able to maintain) and at least 512k per channel of sample memory. Hell, even the dreadful 16k that are offered by some cheap Rigol and Siglent AWGs are a lot better than the 2k of your "bargain".