In many cases Coinbase restored BTC balances of compromised wallets. You don't get that if you manage the keys on your own.
Maybe, but that's not available. The best wallets we have are devices like Trezor.
Yeah, but you can't just rely on those services to reimburse you. If you messed up your computer and effectively granted an attacker control over your coins, there's no way for Coinbase to know that you didn't actually stole the coins yourself. As to the mobile phone wallets, yeah they're not there - yet. But we just need a secret element embedded into the phones' SoC!