Yes, auto withdraw fee are low if you compare it with exchange or wallet fees. But when it comes to faucet, fee looks pretty big. If you are using their faucet only to get free BTC, you need to make over 100 faucet claims to cover withdrawal fee. For example, Faucethub withdrawal fee only 400 Satoshi. If you withdrawing bigger amounts than 0.0002 BTC, fees are even lower.
That is the key attraction to make people use their system as a wallet. If you're doing every day many transactions then you can use their system to save transaction fees but if you're doing once in awhile then no meaning in keeping our coins in an online wallet where we don't have a access to private keys.