Because most people have their own idea of what is morally right in the world, and they want to cling onto that regardless of what other perspectives may exist. Both sides do this.
Also, in some cases, speaking the truth about something leads to them losing their jobs or livelihoods.
“It is difficult to get a man to understand something, when his salary depends on his not understanding it.” - Upton Sinclair
Porn has done it for dozens of years at this point, and it has just become not only an expectation, but just a thing that gets picked up.