(Edit: Hal's explanation fits. People must be sending Faucet coins to the Faucet.)
"people" is me-- when I tweak the Faucet's code I erase my IP address from its database and then have it send coins to itself as a sanity test.
And Hal's right, Bitcoin chooses transactions to spend, not specific outputs (which only matters for sends-to-self, where you own both outputs of a transaction).