Of course and very reasonable, but if the people hiring hides their face wereas asking the freelancers to be videotaped, well... is a red flag. Specially if in the end, nobody is hired for this job.

Maybe is because they are shy, that is a perfect valid reason to me.

Another hypothetical explanation could be that in upwork some well stablished freelancers were targetting new fresh and disperate freelancers hiring then and paying in peanuts to do a job that they then would bill (for a higher amount) to the final client.