If you wish to convince the producers of that, and they are willing, then fine. But it’s up to them to make the decision, not you.
The producers of the show ultimately are the ones in a position to judge how this might affect their bottom line. You don’t know anything about their finances, so you can’t presume the exposure will recoup the costs. If the people who know the costs think it’s a good idea, then they should allow it. But if not, then their wishes should be respected.
“Available to all free of charge,” might work. “Public domain” would mean abandoning their copyright in the central concepts and format of the series, which would be mad.
Along the same lines, I’m surprised that so many movie trailers are still “stream only”, as if the companies care about who sees their commercials and how they see them.
I still remember the Lord of the Rings trailers, which they even created their own torrents for so you could make sure they spread into the torrent world(so to speak) quickly and easily. Now,* they* knew how to advertise the movies.
I think it would be a prudent decision for the producers of a show to release the pilot, but like RealityChuck, I agree that if the producers decide otherwise, that’s their problem (or benefit, if they’re actually right).