I see that a lot of people have given you the obvious inventory answer but for me that's not exactly it.
Instead, it's your relationship with the algorithm that determines your enjoyment with the game. The game is the algorithm, the algorithm is the game.
When you start, you are astonished at this procedurally generated world you find yourself on. Every cave, ravine, lake, animal is some kind of miracle. An hour or two of wonderment later you take off and fly around your starter planet. You realise that it's really all just one biome repeated endlessly. Well, whatever, it's still incredible. You go to a second planet. The colours are different, the flora are different, you see a different building, a different monolith. Wow! It's so new and exciting! Maybe it's barren. Maybe it's lush. It's new.
You build a warp drive and travel to a new system. New aliens! Space battles! New planets! Meeting atlas and starting the main quest! The thrill of the new is still there, 5 hours in. But already you're realising that the pool of buildings you visit on the surface is quite shallow and you may have seen them all, that each planet has plutonium, iron and carbon, that each planet with flora has a 'rock', 'small rock', 'tree' etc. Patterns emerge.
Then the grind begins. Right when you start to see the seams in the algorithm is when you'll have gathered enough stuff that the inventory becomes a problem. The game becomes a drag. You visit planet after planet and see little that surprises you. You learn what the game can and can't generate.
You hit 20 hours. Or 25. Or whenever.
And THEN - here's the thing. You've learned what the game can and can't generate, but only from a limited selection of 20 or so planets. So you convince yourself that you've seen it all - you really believe that - but you've only seen 90-95%. That's most of it. But not all. So now, you go down to a planet, knowing exactly what you'll find... but on that rare occasion that the algorithm throws out an outlier you are now surprised again, just like you were at the start.
At the start you were surprised because you had no idea what was possible. Now you're surprised because you thought you knew what was possible. Massive megafauna, floating jellyfish made of special elements, frozen ice wastes that kill you in seconds - there's a ton of outliers that you have yet to see - and seeing them becomes the point of the game. Seeing rare, beautiful or unusual stuff becomes like getting rare loot in an RPG. And at this point you're not quite as bothered about the lame main quest or inventory worries.
Many people don't make it through that mid point, or decide that whatever outliers and weird stuff the game has left to show them isn't worth it. That's an entirely fair conclusion. For me, it absolutely has been worth it. At some point that will end. But not yet.