Yep, it is great they are doing the big promotional thing ... about time.

But I wish they would do more to encourage their customers to download the Offline Installers and back them up, which are the real preservation. GOG customers as a collective do the true preserving.

Doing the all-in-one download and install with Galaxy is not really game preservation.

When they first released Galaxy I assumed it was downloading the offline installer and storing it somewhere. I was shocked to realize I had to download 50GB for Mafia 3 twice. I deleted Galaxy after that.

They do curate some interesting games in collections during the sales.

Citizen Sleeper 2
Starship Troopers
Run The World Inbetween
Bomb Rush Cyberfunk
VA-11 Hall-A

Some highly reviewed gooduns I've never seen on the main page and very rarely see in little thumbnails on other pages. It's a damn shame that GOG reposts Batman and Diablo on the main page constantly. Of course I love GOG as a preservation repository for marquee titles from big publishers, but indies deserve more of the spotlight since customers can innately invent the word Batman to type into the search bar hoping something about Batman might pop up. But customers can easily never notice Bomb Rush Cyberfunk or the Citizen Sleeper series. Some employee at GOG is bound to have a personal library of the top of the line indie games and they just aren't pushing them into the public eye (except Disco Elysium, which deserves top billing).

Not sure about Batman, probably just a big seller that regularly helps fill GOG's coffers.

Diablo, from what I recall is only available at GOG, so it makes sense to have it placed prominently.

GOG no doubt are in the business of maximizing profits, and that really answers all your questions, especially if as I suspect they could be paid to make certain games prominent on their front page.

What GOG should do, as I have often said, is make the News page a separate one, which would clear up some space, but probably not for the games you listed. GOG no doubt have oodles of games they want to push at us, and profit based benefit would be their guide. Bombard us with two much though, and our minds turn off.
I'm not a big fan of Galaxy, so don't use it myself.

But it can download the Offline Installers for you, just that option is somewhat buried away in the Extras menu. It does not download and automatically install that variant though.

I've seen other stores do at least similar things with "I'm feeling lucky" randomizers. But nothing like this in Galaxy even. Then I looked around and once more came upon my pet peeve that all listings are by default "bestselling". It's way more sensible than amazons default to "Recommended" but still.

Than it occured to me: there already is a large number of possible sorting options, but no "random" option, but it seems to be the perfect place to put that randomness, as it also has the other filters already in place, so you could tailor your randomness very well. Shouldn't take too much work as well to add such a setting.

It doesn't seem random, but most store pages for individual games have a couple recommendation sections down the page a bit, in between the system requirements and the user reviews. They are called "You may like these products" and "Users also bought" (though one or both sections are absent from many product pages). If you visit enough pages for games you like, or are interested in, you should be able to get at least a few ideas for future purchases from these recommendations.
Not saying a "take me to a random game" feature wouldn't be nice, though...as long as they didn't ruin it by weighting it toward certain titles (such as already high-rated or best-selling ones) or publishers, or the like.