The appeal of self voting is obvious, especially when you're a minnow. It can be so difficult to be noticed on Steemit these days with all the vote bots boosting content to the top of the trending page with no quality control at all.
Up voting for me has been a way to add a tiny reward for my effort, which let's be honest, is generally worth more than a cent if you're actually taking the time to try to add value to the platform.
Having said that, I haven't being upvoting my comments. I think the difference here is that accounts with larger amounts of SP can catapult their comments to the top of the comment section even if the author/other voters don't want that to happen.
I think it's great that you were given the chance to build your account through such generous delegations. Did you ever find out why they had both delegated so much to you?