It's highly likely the studios themselves release those annoyingly watermarked versions.
First of all releasing the thing for free but pretending it's just some chinese will make it unlikely anybody else is going to buy the video just to put it online again without a watermark.
Second, the watermark is made to be that annoying on purpose, to make those that really want it more likely to actually pay.
Third, the watermark isn't completely ruining it but also the video is not HD quality either, so they get people to slowly get used to and enjoy their JAVs until they eventually consider buying those they want in better quality without watermark.
When you think about the production cost of a Video... just making 1 video takes time and you have to buy the equipment. But they make thousands of videos and they have experience and reuse the equipment, so the cost for a single video will be reduced dramatically to the point where they already make a profit if the average consumer watches 99 of them for free and just buy 1. Thanks to digital releases they don't even have any distribution cost.
So ultimately it makes perfect sense for them to follow a strategy that literally throws out 99% of their content for free while also giving the potential customers an incentive to actually buy something.
No.