[thwarted]

This is the trend because the existence of the brand's website as a multi-seller marketplace is considered more valuable/higher ROI than the actual direct selling of items. And that's a reasonable view considering most of what is being sold is commodity and prices, thus margin, having downward pressure. The e-commerce website gets a positive reputation and a brand is built for being a good place to buy things, so it expands into being a hosting platform other sellers, with the intent of drawing more customers based on the brand reputation.

[jamiek88]

At the risk of long term diluting that brand reputation.

[thwarted]

Yes, but the brand, being non-tangible, has stronger staying power as the platform marketplace expands to encompass more sellers. The brand then becomes more powerful as it eats up the reputation of the individual sellers.

Additionally, no one gives a crap about long-term anymore. Scorched earth, grab what you can, screw everyone else and all that.