How do Community Cross Posts work?
Why don't they show up on other Hive based interfaces?
Some know this feature as simply "Cross Posting" but to be specific it is **"Community Cross Posting" **
It is a feature specifically to share any hive post inside a community.
To share a post on your own personal blog use the feature "Add to Blog"
HOW TO ADD TO SHARE/CROSS-POST TO A COMMUNITY
1. First check community rules to see if Cross-Posting is allowed.
It really is up to you to make sure it's allowed in the community. Some communities allow it... some only allow moderators to cross-post and some don't allow it. Breaking the rules risks having the cross-post removed and perhaps having your account muted for breaking rules.
2. Go to post
3. Select Cross post in...
4. Pick the Community add a message
PeakD only lists communities that you are subscribed to.
The message is important as it gives readers a reason as to why you are cross-posting AND more importantly what their comments should be about.
A cross post has it's own set of comments unique to that new community.
You are creating a brand new post on HIVE
That post is pretty empty but it does indicate that it is a cross-post and it links to the ORIGINAL post.
Peakd.com then fetches the information from the original post and displays that.
The cross-post itself has rewards declined
PeakD.com forwards votes for this post to the ORIGINAL post
Much of the information shown about the post comes from the ORIGINAL
After the original post has been around for 7 days the vote button recommends tipping
These cross-posts will show up in your own ALL POSTS page
Users can interact with your cross-post (default) and can also interact with the original on PeakD.com
Other interfaces have mostly not done the work needed to support cross-posts as of yet. Cross-posts is an open decentralized system and any interface is welcome to add support.
If any interface is wanting more information we would be happy to give them support and help them with code.
The community has largely suggested to decline rewards to the new post and direct it to the original.
@peakd. Main authors presently: 
@jarvie