Why do fixtures within the same store have the same template and the planogram?

A planogram template is always shared for a group of fixtures that have the same category, the same number of shelves and the same category variant. So if you are seeing the same planogram template for all fixtures, it is probably because you have not filled in any category variant for all of those fixtures.

Shared template 

Where do you set a category variant?

Category variants are set in the Store Editor. In the floor plan you have to activate the fixture for which you want to set the variant and then set the Category Variant in the Fixture Properties tab.

Setting a category variant