This has been discussed a couple of times before, but the conclusion each time has been that expiring votes a) pose a security risk. I.e. whales go on a vacation, forget to vote every X days etc; and more importantly, b) stakeholders should have the right to vote however they want. Various solutions have been discussed, if there's a good one proposed, I'd support it. But it's not top of my list right now. I have to say that DPoS is trash, but unfortunately, replacing that is a really tall order. So, I'm being more reasonable here and just asking for more pressing changes.
PS: You can follow the discussion here: https://github.com/steemit/steem/issues/953
You are indeed far more reasonable in your demands than am I.
However, the claim that expiring votes is a security risk seems facile, and the fact that content is not evergreen seems to establish that such control of votes is not difficult to effect. I don't doubt that it has been put forward, but doubt less it could be trivially done.
Regardless, you didn't do it, aren't responsible for it, and certainly have a better grasp of the issue than I.