clarry: Plenty of abandonware sites and torrents to a great job of keeping old classics as well as unhread of games alive. And archive.org has a collection of about 4000 DOS games, larger than the entire GOG catalog.
Smannesman: That's not keeping it alive, that's necrophilia.
And that's being somewhat arrogant. Abandonware is not an ideal state of affairs, it's not a clean-cut legal concept, but it is a necessary evil that compensates for a fundamental problem in intellectual property law - when copyright is no longer used for its intended purpose, namely to enable creators to earn a reasonable living from the fruits of their labour, and simply to suppress the existence of past works.
Many of the games on abandonware sites are legitimately "abandoned" - in many cases because the rights to them are so dispersed over multiple disinterested owners (usually because the rights holder ceased to exist without transferring the rights), certain external IPs require re-licensing (cars, football teams, movies, likenesses) that is either prohibitively expensive or impossible because other parties have licensing exclusivity.
I appreciate GOG for the ability to buy out-of-print games legally at reasonable prices, and I appreciate publishers like Night Dive and Tommo for their efforts to track down and consolidate dispersed rights. But for GOG, it's usually only profitable to go after low-hanging fruit (mostly games where the rights are held by a single rights holder), whereas the effort and expense that publishers like Night Dive put in to recover and consolidate the rights to long-lost titles really only pays off for the highest profile titles, and as we see with stuff like No One Lives Forever, there's no guarantee that it's even recoverable in the first place.
If we lived in a perfect world, GOG would acquire every single classic game out there and offer it for sale in perpetuity. We don't live in a perfect world. Sometimes games are so niche and require so much effort and so much expense to buy out rights that the chances of a renewed legal release are basically zero. Copyright law fails to acknowledge this. It is antiquated and assumes that games, movies, music and books are exhaustible assets with limited shelf lives.
Also, in a perfect world, we'd be buying these classic games to support the original creators. In reality, the original creators very rarely see a dime of the income from these digital releases - it's the publishers that are profiting here.
So yes, abandonware sites - at least those that have a healthy respect for publishers and developers that still want to sell their games and actively remove titles that are being actively sold - do as great a job in preserving access to old classics as GOG does. Dismissing such sites out of hand is a demonstration of extreme naivété about how the gaming industry works.
