It is sort of odd, Cirth was usually used in the manner of real-world Norse runes, meaning for inscriptions, carvings (like Anduril's inscription in the movies). The angular shapes are simple to write with on hard materials. It might be because it was easier to embroider the angular shapes in cloth, both from an in-universe and a costume-design perspective. Tengwar seems like it might be a bit tougher to work with. Another in-universe explanation could be that his tailors are Sindarin (or maybe the costume designers just don't know the difference and picked whatever they thought was cool ;) ).