I suppose if it was explicitly listed as 'Stolen 40" TV!' in the 'Stolen Goods' category of eBay you could say that they should have known, and if Paypal had special 'funds to buy stolen things' accounts and one of those was used to buy it, then you could put some blame to them, etc.
But how far away do you project the blame from the actual criminal? If Udemy is responsible, then do you absolve the person who pirated and uploaded it of guilt? Or do you divide and dilute it? How long does the chain need to be before each participant's share of the guilt is so small as to be negligible and irrelevant?
Why not instead blame the person who uploaded it to make money while knowing that they hadn't created it and didn't own the rights?