I'm not sure what you mean by 'transition'. Do you mean how do mega-links, torrents and such make it on to these thread pages? I'm relatively new here, so I can't speak to all of it, one of the mods or veterans probably knows more. Personally I just assume that one of the developer's Patreon members downloads the game directly, uploads it to either a P2P-site (torrent) or file hosting service website (keep2Share, Fileboom, etc.). That person then shares the link to these websites here, for members to download.
I think it (highly) unlikely that developers will share their hard work for free. Though if you think about it, most (popular) game developers likely assume that their games are gonna end up being downloadable for free eventually, if not almost immediately after release. If you look at it from an economic standpoint it could be an effective way to market your game to people who otherwise might not (be able) to see it. Even though they didn't pay for that particular version they might be so enticed/excited about it that they sign up through Patreon to help the developer develop it further, and get early access. Nevertheless no developer is going to actively encourage use without payment, even with a side-benefit, like greater exposure. Doing so, would eventually see diminishing returns for him/her/them.
I'm just spit-balling here, perhaps even rambling a bit. This is just my sense of how things work.