It is, but the carbon actually in the plastic is a small portion of the total carbon used in the production process. Chucking it in landfill in a situation where you could otherwise substitute for new plastic means that the cost of chucking it in landfill is the total carbon cost of the new thing.
Recycling plastic is almost never worth it. You have to plan for it while designing the original artifact manage the chain of custody, and finally find an application that can actually use the reprocessed plastic.
