Even though not exactly "income", one way people passive profit is in the appreciation of the token.
Since we all feel STEEM is going to much higher levels, simply buying, powering up, and HODLing will net one a fine return.
Also, when powering up, it makes one more powerful including on self votes. So this is akin to the bots you mentioned, not really active or passive but it does equate to more STEEM in one's wallet.
Thanks for the comment and for showing people even more ways to earn through Steemit. You're right, hodling and powering up is definitely one that I overlooked and is worth a mention,