Steem-UA ... It is based on the number of followers you have and the level of engagement surrounding your post. You can only get 'shares' by delegating to them.
my 5 cents: I have a decent followers number (around 180) and sufficient 'engagement surrounding my posts' (it is all original, and rewarded content, people upvote it cause they like it, I believe)... amount of delegation to this service: zero. number of the posts upvoted by the service: zero. i.e. they curated not a single post of my blog.
due to these details, I assume this service is based mostly on the delegation. prove me I am wrong, hehe.