Why isnt a culturally significant game's source not considered public interest? Especially when the game is no longer being sold?

In this particular and narrow instance, it does seem like Blizzard is making good on going back and updating and maintaining the old code. You can argue the reasons, I suppose, but this seems in line with exactly what copyright is supposed to be protecting here. They're reviving support for the game, updating it for modern machines to receive, and making the previous iteration accessible.

I would love to have it to, but it's hard to fault Blizzard here for anything but "hey it would be really nice if you..."

There is still a vested interest in protecting this game from Blizzard's point of view, and it sucks, but in this case they have a fairly good justification and have been holding up their end of the bargain (re-releasing)

They've been real champs about these older games, like Diablo II getting updates. My heart skipped a beat when we finally got a native OS X client update that wasn't a Carbon app - that was really going above and beyond in my opinion, and their support was great for it despite the hiccups on release.

It was being sold up until about a week ago. I'm sure that you can find a store that still sells it on CD.

Blizzard is making a StarCraft remaster right now; who knows how much original source is still in there. My guess is probably a lot, since they want to keep the same mechanics.

Because they might want to withhold their right to milk it for successive generations and not have to bother with making original games.

Parent's usage of "Interest of the Public" here typically means "the welfare or well-being of the general public; commonwealth" and you seem to be meaning the "lot's of people are curious -- culturally significant" kind.