>The problem is that the snap store is managed by Ubuntu without any community oversight.

That is already the case for most repos/launchpad on Ubuntu but people don't really have too much problems with that.

>By not releasing source code to the store, other distributions cannot create their own.

Other distributions wouldn't because the operational cost of operating it is too high.

>These are the reasons what is holding snap back for broader adoption.

Snap isn't being held back by adoption. It has more first party publisher support and more installs.