What can cause an Index "total writer" to be the same in every index?
Unless an index is filtered, they should all be written to the same number of times under normal DML activity. 

If a row is updated or added, any columns in any index must also be added/updated.

So you should not expect some indexes to be written to a different number of times, unless you are reorganizing or rebuilding individual indexes specifically.

Also, please read this post over on SQLPerformance.com:


Don't just blindly create those "missing" indexes!