The game still has rules and systems to facilitate how the player will achieve those goals, because that's what makes a game fun.
Yeah, one of those being automated redstone contraptions. I was fucking around with redstone in 2011. I didn't find it very engaging so I didn't continue using it, which is my prerogative as a minecraft player. Tech mods are far superior.
It becomes very boring if
Uh...
Yes, it's a sandbox where the point is that goals are directed by the player themselves
You defeated your own point. If you dislike the existence of automated farms then just don't use them. You're not forced to use them, you're not forced to do anything at all. At the end of the day that is the game's biggest strength and its biggest weakness. You might find caving fun, other players do not, and so they use farms to stockpile resources for big builds, which themselves would otherwise be arduous to gather materials for the "normal" way. But that way is only normal for you, because you see their way of playing as abnormal.
You don't even need to kill the dragon to get flight, just bridge out to the islands and find a city. If minecraft was the kind of game that forced you to kill the dragon before you could reach the cities to obtain flight, you might have a point. But it isn't, so you really don't. Essentially you are complaining that other people are having fun wrong.
But even then, think about how you reach the dragon in the first place. You first go into a cave and get diamonds, which is normal. Everything after that is completely retarded and not explained at all, because minecraft is not a normal game. You pour water on lava which makes obsidian, mine some which takes forever for some reason, arrange them very specifically, then (for some reason) light it on fire with flint and steel (iron). This is so retarded that they had to add ruined portals to the overworld, years and years after the nether update mind you, to kind of maybe hint that you're supposed to arrange obsidian like that, but it still utterly fails to add meaningfully to the so called core gameplay loop at all. The truth is that minecraft grew by word of mouth, and that's also how almost the entirety of its mechanics were explained to players. The developers didn't explain any of this anywhere in the game, the players did. And this was way before microsoft bought it. In that same vein, the players also figured out the rules for spawning mobs, and how to automate the production of the resources they drop. How can you say that one of these is fine and the other isn't? It makes no sense.
Anyway, then you go to the nether and find some blazes after much searching (or leave because you don't know what you're looking for and the world is massive). Eventually you find some (maybe after finding a fortress without any blaze spawners and assuming they are pointless, being forced to find a second fortress and be lucky enough to stumble on some blazes) and then craft the rods into powder which is normal I guess because you just randomly try things. And I guess if you're just randomly trying things, you can eventually maybe stumble on the recipe for eyes of ender by systematically going down the list of items that you try to rub blaze powder onto. (Or you can just look it up like a normal person). Then you try using one, and it floats up into the sky. Eventually you figure out that you're supposed to follow it, even though it takes forever to float up and then come back down, so after some more fucking around you find the stronghold. Then you have to go back and find more blazes because you had no idea that you needed like 8 eyes, plus any extras that destroy themselves on the journey, to complete the portal. If you even think to use the eyes on the portal at all. Oh and by the way none of this traveling is helped in any way by any worthwhile mapping mechanics, and the world is massive, so have fun writing down coordinates (if you found out from the internet that you can press f3 and get coordinates to orient yourself).
After all of that, then you're teleported to another dimension with a dragon and you're fucked because you didn't bring a bow. How exactly was caving for resources supposed to prepare you for this? It wasn't. Looking it up online, or having your friends tell you, is supposed to do that. And they will also tell you to make a farm after you get bored of caving for the 20th time.
If you just throw up your hands and say "The game has no point! There's no core gameplay loop! Do whatever you want!" then it begs the question of "Well then why don't I just go build something in a CAD program?" It'd be like running a DnD campaign where you tell the players "Do whatever you want."
Well...
it's a sandbox where the point is that goals are directed by the player themselves
If you like caving and then depositing your loot in a base, and then doing it again, then that is your core gameplay loop. If you like building farms so you don't have to spend time caving, then that is your core gameplay loop (essentially you are playing a retarded version of factorio but there you are). If you like neither of those and just like exploring the landscape so you can take wholesome chungus screenshots to post on reddit, and build a shit hut once in a while out of dirt and twigs, then that is your core gameplay loop. Because it is a sandbox and has no point.
Which is why gregtech is superior.