Aliexpress is a B2C marketplace that directs its offer to consumer clients.
For this reason the vendors that you will find on this platform are merchants, just like you. They then buy their products from a manufacturer and sell through it through Aliexpress.
uDroppy doesn’t partner up with ordinary merchants, but with actual manufacturers and qualified agents that can assure a correct and reliable execution of the tasks that belong to this part of the supply chain.
It is not theoretically impossible for a supplier that works with uDroppy to open a shop on Aliexpress and sell his goods, but it’s very unlikely to happen as selling directly to consumers is not part of the business plan of these entities.