I am using vanilla 44.12 but haven't seen a change in bins since before 43.05.
You have over 10 idlers so the bin-related jobs should be assigned (unless you have some burrows restricting your dwarfs from the areas).
There can be two bin-related jobs per stockpile that you can find in the job list.
This is my fort's job list:
On your job list, you are looking for a "Store Item in Stockpile" or "Store Item in Bin" job with your iron bar stockpile's number on the right.[/i] The process works like this, if there is no empty bin on the stockpile, a "Store Item in Stockpile" job is created to bring the bin to the stockpile, and if there is a non-full bin on the stockpile, a "Store Item in Bin" job is created and slowly adds items to the job then a dwarf is assigned to the job. Here is an screenshot of 'j'View_Job details for one of mine:
To do the job in that second image, that dwarf will take a month to walk all over and collect all those bolts then bring them all to the bin, maybe two months.
A short warning: Storing ammo in bins can cause message spam if you are not careful in your setup.. So, looking at your setup, there should be either a "Store Item in Stockpile" or "Store Item in Bin" job related to the iron bar stockpile's #. You should be able to 'j' on that job to see what items are involved.
There is at least one bin on that iron bar stockpile.... What's on your job list?
Also, I typically set a stockpile bins to max, because only one is brought at a time.