What would be the incentive?

To get more funding for their work, more fame within the parapsychology community, and to make it more likely that the world at large will realize the truth via "fake-but-accurate" experiments. Some parapsychologists pay for their own experiments, using resources garnered from a "day job" in some other field, but many rely on donations from wacky psi-enthusiasts (people who also get excited about ghosts, "subtle energies" and so forth), or selling psi-controlled meditation lamps. Many others think that it's critically important for mainstream funding sources to provide grants to parapsychologists (such as themselves) to do the work they find interesting and important.

Under those circumstances, a psychic believer could come up with all sorts of justifications:

I have to publish these "fake but accurate" experiments to convince others of the effects that I KNOW are really there, and thus gain enough resources to get definitive proof. After all, surely those dishonest skeptics and materialists (who regularly misrepresent the existing literature, and deceive the broader scientific community about the great work done in parapsychology) are doing the same thing, and if only one side 'enhances' its data then the truth will lose out.