What the other places are doing to remain Reddit "clones", rather than "alternatives", is they refuse to change the basic mechanics.
Most sites being advocated are just reskinns of the Reddit backbone. They still the same downvote and upvote system and the same subreddit system, except that they are renammed to something different. They still have a front page that looks different, but still gets its content by ranking posts by the net number of upvotes, which degrade over a number of hours. They still have a system that lets you join groups of similar interests, but it controlled by who creates the group first. They still follow the same basic formula that Reddit uses, but just change how it looks and what it's called.
In some cases, just a simple rebranding, with the addition of a few improvements, is enough to take the userbase of a different site. After all, Reddit is very similar to Digg, before it changed. However, when a problem exists in the foundation of a website, it's impossible to solve it by building a new house on top of it. Voat still allows moderators, which means it's still possible to have someone ban content that they don't like. Empeopled is still using a system that allows people to upvote what they like, and downvote things that they don't agree with, meaning that shitposts are still going to hit the front page, and will even pay the posters when they do. As long as there is a crack in the foundation, water is still going to get in.
What Hubski does is retains the strong points of Reddit, while changing the things that don't work. There's no moderators that can silence opinions that they don't like. There's no upvotes to reward people that spout popular opinions. There's no downvotes to punish people for going against the grain. There's no karma system that gives the upvotes and downvotes weight. Hubski still has the ability to track and rank the popularity of a post, but the success of a post doesn't really change the track record of a user in a way that would commend circle jerking and discourage discourse.
These other sites are refusing to offer enough of a change that would make them more appealing than Reddit. At the end of the day, they just wind up being Reddits, but with less content and comment, which drives people right back to Reddit.