If we ignore everything else like all of the entities that would exist in those chunks, and just care about blocks, a circle of 32 chunks around the player has over 210 million blocks. Having a lot of chunks requires a lot of computational power.
Minecraft, at least the Java edition, is also terribly programmed and is super inefficient in a lot of its code. It’s gotten better than it was, but it’s still not really that good or efficient.
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