It's because Hondas and Toyotas of the period did not have anti-draindown circuitry that in other cars shuts down the battery preventing a total draindown. Likely causes are a duff battery (at 6 years old, could be that); Bluetooth problem (searching for a paired phone no longer available: Cure to remove all old pairings from the list); locking problem (car not locking properly and immobiliser not setting); radio problem (radio not completely shutting down). But the most likely reason is the 'follow me home' lighting that leaves the interior light on after you take the key out. Even though the light eventually goes out, the circuit remains live and drains the battery. Cure: switch the interior light off completely so it does not go on when you open a door.