Buying online direct from the manufacturer? Almost everyone sells direct. Use Amazon to find the seller and then contact them directly.
Amazon delivers next day or the same day many of the items if you have Prime.
I tried many times to order something directly, and most of the time it’s the same price and longer shipping. So, for me in terms of convenience Amazon wins.
Why would I do that? Now I’m spending time verifying individual random brands all to get the same price (plus shipping)?
What if you want to buy simple Chinese plastic stuff (e.g. someone elsewhere mentioned zip ties)? The manufacturer is somewhere in China with a minimum order of 10,000, so no, you can't go to them. Amazon is often the cheapest source for this, cheaper than any local retail.