A lot of people abuse this legal loophole in Steemit. I've had it happen to me ... and yes, it's really annoying. For someone to come in and upvote his four word comments and not leave a thing on your post says something about his character -- to me.

On the other hand, sometimes it's appropriate to upvote your own comment if you've spent time on it, you think it adds to the value of the conversation and you'd like to push it up past a LONG line of previous comments. If you don't do it often and you also upvote the post, I don't find that offensive.

However ... here is something else to consider:

Whales (and many dolphins) don't come to Steemit to create content. They're here as investors -- to make money from their stake. And if that's the case, then there are four paths open to them to profit from their involvement here -- other than waiting for the price of Steem to rise.

1. Curation -- not many whales have the time or patience to wade through post after post trying to find something worth upvoting -- and then settle for a fraction of the 25% curation reward. If you have a gob of money and a life ... and other interests, you can see why this isn't appealing. (Also ... sad fact of life: Not many people become whales by being philanthropists. They know how to look out for Number 1.)

2. Self-upvoting comments. Easy. Lazy. Works great though.

3. Vote selling. Kind of a gray area for those who don't agree with the bots / vote-buying.

4. Delegation leasing. Potentially real profitable. Kind of a hassle to administer. Takes a week for them to get their delegated SP back once a lease expires. Can't lease it out again in the meantime.

So ... you can see why some do as they do. Also, you don't have to be a whale to profit by upvoting your own comments. (You also don't have to bother with pesky stuff like making decent posts.) As I said. Easy. Lazy. Self-serving. And yes, potentially very annoying if not done for the reason I mentioned at the start.