Steemit always intended their stake to be non-voting, in fact they implemented a feature into the blockchain code to enforce that. For various reasons the feature was never used, but the tradition of not voting with their stake remains. That tradition exists for a reason, at least historically. With the dominant stake they once had, if they did vote, no one else would have any meaningful say at all in anything. So for that reason, and because the stake was mined for the purpose of funding the company, compensating their founders, and giving away to new users, they have never voted (apart from a few specific exceptions, mostly emergencies).

Even despite that tradition, they do delegate a large amount of stake to steemcleaners and some other downvoting efforts. It simply numerically isn't enough. I haven't done an exact calculation but my intuition is that bidbots alone have more stake than Steemit (recall that Steemit has sold a lot and continues to sell a lot; the meme about Steemit having an absurdly dominant stake like 80% as they once did is complete wrong), and bidbots are not the only problem.

Trying to solve this the way you suggest would not work and has not worked. Working against the underlying incentives by trying to tell people what you think they should do with their stake despite incentives encouraging them to do something else is inefficient to the point of ineffective, even if you are ultimately right in a way. It is like trying to push a car uphill several miles to get to a repair shop but collapsing from physical exhaustion before you get there, when you could instead roll it downhill to another shop at the bottom of the hill.

I share some of your lack of certainty about whether HF21/EIP will produce the intended and desired results but I think they are worth a try. We should have tried making such improvements long ago, but since we have not, there is no time like the present.