Its more like every byte should have entropy in it. When you limit yourself to a single byte of entropy, you only have one byte of possibilities to guess (256 possibilities), when you should have had 384 bits of entropy, now you only have.... 8

Its the range that changes.

you can either try and guess the key from

range(0, 255) (which is easy!)

or

range(0, 39402006196394479212279040100143613805079739270465446667948293404245721771496870329047266088258938001861606973112319)

(it exceeds the heat death of the universe)