Sometimes they are lies. Governments including Western ones have lied before (e.g. Tuskegee Syphillis), and academics have published flawed, misleading, or straight-up fabricated studies (e.g. “landmark” Alzheimer’s study).

But more often, the “fact” does not address the individual’s issues, and the individual may give a stupid counterargument (“…lie pushed by my enemies…”) but they have a legitimate one. In this case, I guarantee there are specific people who’ve been indisputably replaced by H1Bs, maybe clustered in specific reasons, and maybe specific fields. Telling these people “overall H1Bs create jobs” won’t convince them.

Like telling poor people “the economy is improving, inflation is only 0.x%”. Both may be true in general at the population level, but to the person you’re speaking to, they don’t matter; economic improvements can go to others while they suffer more.