It's true that just about every veteran 3D hobbyist who wants DS4 Pro for free has downloaded it by now, or at least now has it in their "purchase" history in case they want it someday.

The "DS4 Free" extension wouldn't be for them. It would be to dip into the constant flow of new hobbyists. People who wander onto the Daz or Rendo or RDNA sites, see some cool stuff, and think "Hmm, I'd like to try that." Newbies spend the most $$ once they get hooked. That's what Daz is trying to cash in on. If any of us oldies with bloated runtimes decide to buy some Genesis / V5 products as a result of this giveaway, that's just gravy.