Many good points have been brought up, and I'll just link to them here, for ease.

Source: I work at a credit/debit card transaction processing company on the Database and Processing Software teams.

1. Security

See mhoran_psprep's answer.

2. Tradition

See Chris' answer.

3. System Integrity

Believe it or not, banks don't expose their primary (or secondary) database to end users. They don't expose their fastest / most robust database to end users. By only storing x days of data in that customer-facing database and limiting the range of any one query, any query run against it is much less likely to cause system-wide slowness.

They most definitely have database archives which are kept offline, and most definitely have an employee-facing database which allows employees to query larger ranges of data.

4. No Added Value

What would a bank have to gain by allowing you to query a full year of transactions?

Why don't banks give access to all your transaction activity?
In the Honor Harrington universe, ship-to-ship combat takes two forms: missiles and direct energy weapons.

Missiles come in two forms - bomb-pumped lasers and contact nukes.  Both use multi-megaton nuclear initiations to damage enemy ships.

While this sort of event on a planetary surface will obviously have lasting effects, what long-term effects could be expected in a vacuum environment, aside from the destructive force associated with the explosions themselves, and the resulting EMP?  Especially, would there be lingering (or spreading) radiation?
