Shipping from 1 seller will be combined just like any other selling platform. If you buy from multiple sellers then of course you pay each seller shipping for the bunch of items you're buying from them. It's the same as eBay or Amazon. The problem is almost nothing is on Amazon beside popular western products and scammers/resellers etc. On eBay you get plenty of Asia made products but not everything. On Aliexpress you get a lot of items you won't find for sell elsewhere, at least not on English speaking sites. After that you're either on Alibaba direct to supplier or one of many Chinese encrypted websites. If you can't find it even there then you gotta go to China for it XD
Shipping offered varies per seller. For cheap items, free/cheap snail post is what I use, for expensive items a DHL may even be necessary with no cheap shipping available.
Many things can be found direct from Asia at reasonable prices while you would have to pay arm and leg for it locally, or you can't find it locally at all is far more common anyway. The whole manufacturing supply chain has moved to Asia thanks to stupid politicians.