So is it possible for 1 seed to generate all of them? Doesn't that break information theory (Shannon's compression limit)?
From that seed you can generate for all practical purposes an infinite number of private keys for any and all purposes in existence. Using cryptographic one way functions such as a hash or PRNG.
Example: truncate_as_needed ( sha512 (seed | 2022 | wallet_title | priv #123) ) = private key #123