Because Home Depot sells them in the store too just as my friend did. We don’t have IKEA here so not sure on them.
Let me tell you:
The same size kitchen cabinet set sold in Home Depot would have been $10k, I'm sure it is high quality and name brand. The same size IKEA kitchen cabinet set was $2600, it is lower quality for sure and I have to assemble myself (let's say $1k labor) but if I scratch it I can just run down there to get a replacement same day. Installation let's say Ikea is harder to install and take an extra $1k (my contractor charge me $2k to install in 3 days, so I cannot imagine Home Depot will cost even more than that).
How much do you think your friend is selling cabinets for? How much do you think Amazon is selling for? You can blame your business failure on anyone but, what I learn in my kitchen remodeling saga, is that it takes a lot of relationship to build and install them, warranty them, return scratched up units and make things right. They would not want to deal with Walmart and definitely not Amazon when things hit the fan. I have seen vendors selling countertop fabrication at a loss to sell cabinets to make it up in profits, I see them refuse to sell just the cabinets to others to install because they cannot guarantee not damaging them.
This "Amazon put my friend's cabinet business out of business" argument, is like saying Goodman furnace selling on Amazon is putting your local HVAC tech out of business. I am not buying it.