Q.Why does the Ledger require balancing, but the Journal does not?

The two books serve different purposes, and only one of them is built around individual accounts that can meaningfully have a 'net position'.

The Journal is organised chronologically — every transaction, involving whichever accounts happen to be affected, is entered one after another purely in the order it occurred. There is no natural grouping within the Journal that could be 'balanced', because consecutive entries in the Journal usually relate to entirely different accounts (a cash sale, then a rent payment, then a credit purchase) — there is nothing to net against what.

The Ledger, by contrast, is organised account-wise — every single transaction that has ever touched a particular account (say, the Cash Account) is collected together in one place, on both its debit and credit sides, regardless of when each transaction happened. Because all the debit and credit entries for that one specific account are gathered together, it becomes both possible and meaningful to net them against each other to find the account's net position — how much cash remains, how much a debtor still owes, how much of an expense has accumulated. This net figure (the balance) is exactly the inf …

Saying 'the Journal is balanced too, by checking total debits = total credits' — that is a different check (verifying the whole Journal's dual-aspect equality), not 'balancing' in the le …