The whole point of crypto is that you hold your private keys. Putting them on google may be 6.5/10 safe but not as safe as you can get. Maybe its different with Steem, i'm new to the platform, but with my other crypto private keys i would never store them on the cloud. Usually on a hardware wallet like the Trezor. Another thing I thought of are the recent articles of people being frozen out of their google docs because of some sort of the content of their documents. I just think better safe than sorry.