Why Cine lenses are expensive (from biggest factor to smallest):
1. Supply vs. Demand: Photo market is way bigger
2. Breathing and Cam-driven internal construction
3. Still photo lens zooms are “vari-focal” meaning they change focus with zoom
4. Light transmission (T-stop) and color consistency across a series
Cine lenses have a wider angle of rotation on the lens for adjusting focus. They are geared with the standard .8 MOD pitch and the spacing along the length of the lens of the focus gearing is consistent between multiple lenses (you don’t have to move your follow focus after switching focal lengths).
Photo lenses are held to if anything, a higher optical standard in many ways.