The original producers are part of the primary market, and only pay attention to the consumers that participate in the primary market. The secondary market--where open sharing of "used" content goes on--is ignored by the primary market.
The primary-market producers for exploitative pornography consist mainly of two types: individuals who film their own acts of exploitation to use as currency in trade for the films of exploitation-acts of others; and professionals, usually members of a crime syndicate that has humman trafficking business, who sell their content on the black market in less reputable countries. In both of these cases, the produced works are scarce goods: as few people will see them as can be managed.
Leaks to the secondary market are bad for the producers in the primary market; not only do they increase supply for the consumers in the primary market (and thereby drive down demand), but they also make it much more likely that law-enforcement will get their hands on the offending media, and be able to analyze it for clues to the individual or group's whereabouts, or just as proof in a trial. Thus, the producers in the primary market tend to enforce a loan-shark-like "you break my trust, I break your knuckles" policy on the redistribution of their content.
The incentives are basically just entirely missing for anyone in the primary market to specifically release content to the secondary market. Anyone who "just wants the attention" and releases multiple videos will soon be tracked down and arrested.
Picture it like someone who is manufacturing some form of illegal-but-sought-after drug, like MDMA. Have you ever heard of someone who makes MDMA--not a redistributor, but an originator--giving away large quantities of it to people they don't know, just for the attention? That's just throwing away your assets, your safety, and your profitable business all at the same time, isn't it?