Sounds like a weird decision. From what I've heard post-September, South Africa was for a while rumoured to be the best replacement destination for some of the lost transatlantic traffic. So several airlines allegedly upped their capacity on those routes.
Does anyone know what routes the planes will be used on instead?
CPT is notoriously seasonal - massive peaks in the northern winter, and huge troughs in the summer. Load factors shift enormously during the year on CPT. This may account for TK's decision to stop their CPT tag.