Glitters (or glisters) in this case is not a noun but the verb to glitter (or to glister). 'All' is the noun, which is a mass noun that takes the singular form.

Glitter is commonly used in arts and crafts to color, accessorise and texture items. The small, brightly colored particles often stick to clothing, skin, and furniture, and can be difficult to remove. It is also used on optically variable inks.

Glitter can represent what is fake, not real. It can remind us of our materialism, hoarding treasure, shiny resources that are fought over, a symbol of greed, a source of conflict and war.