Can't keep a marketplace at the same level of standard as a direct seller. Selling millions of products doesn't seem to scale well. Worked for books, but even there, opening the door to seller accounts flooded the lists with copies, a ruin for publishers who touched the devil rather than staying away from it.
I like amazon for many things they do well, but the truth is that they were never profitable with their previous business model. Now they've been turning directions to make a profit, it's the snowball to their death.