It's more that AliExpress is all over the place, which is probably because manufacturing in China is itself all over the place (small and pretty much amateur-hour cottage factories doing plastic molded stuff or pretty simple electronics right next to much bigger professional companies designing their own smartphones and computers) plus there is very little in the way of established brands and without a brand to defend, manufacturers don't really care if customers get a bad impression of whatever product name they're using today for their, at best, badly made stuff.

It also doesn't help that in a lot of domains competition in China is mainly on price: the manufacturers might even know how to do a good product, but they have to use inferior parts and cut corners on their designs to stay competitive on price.

(At some point I looked into importing LED light bulbs into Europe from China and got and evaluated several samples and then went back to the manufacturers and at least one e-mail exchange was very enlightening on this and on just how little extra money it actually costs to provide a much better product, but to compete they have to advertise - this was in Alibaba, the B2B site that gave birth to Aliexpress - the cheapest product they have which is kinda crap but only a domain expert doing a teardown of their product will spot it).

Also the fraud prevention in AliExpress is pretty much non-existent and anti-fraud there is entirelly reactive, so product listings with fradulent claims which are hard for customers to validate just stay there forever (for example, almost all powerbank storage claims or solar power bank supply claims are complete total bollocks, insanelly so at times - I've seen listings for small powerbanks claiming more power storage than actual EV cars have).

So for some things you can get really decent stuff at a good price - best place to buy switches or push-buttons for Electronics and as the above poster mentioned mini-PCs, to which I will also add Single Board Computers - whilst in other areas it's a bit of a crap shoot if you'll get something decently made or not - for example clothing - and in yet others the scams are more than the honest listings - such as external digital storage, solar power or power storage.

You'd be surprised, actually. You have to be careful, yes - the default option is that you get crap - but all of the high-quality cycling gear/running gear/variety consumer electronics I've scored is a testament to the possibility of getting great stuff.