They can stop printing. But it is hard for me to defend Amazon, Ebay, et al with 'they can do what they want on their platform'.
If your argument is that eBay and Amazon are so critical to the fabric of the internet that special rules must apply to them, I wholeheartedly disagree.
I do think, however, that the current situation is no longer acceptable. I don't know whether as a society we should consider some sort of limit on influence a given company has, but that is actually what is needed. If Ebay was a corner store, I would not give half a shit that it stopped carrying Seuss. When a publicly traded company does it, it quickly becomes problematic.
The freedom of a giant, monopolistic company is not aligned with the freedom of humans.
We already have precedents for conpanies being forced to impartiality- utilities. Ebay's a utility, the modern large-scale version of the ground a flea market sits on.