The big reason all high end cameras aren’t video cameras are mostly taxes in some regions and lazy product differentiation.
If you're a youtube creator, these cameras can make you look "pro" for a small budget. The price points to entry because of this type of gear brings the creation market to a much wider market, which can be a good thing. Bringing this gear to a full camera crew with DP, AC, etc makes integration harder. Good times!
Though you definitely hear about productions using them anyway.
- Cine zoom lenses must provide a fixed point of focus when you are zooming. This leads to a more complex mechanism.
- Different cine fixed lenses in one project usually must have identical image quality. That is why they are produced in series (for example 'XEEN PRO Cinema Lenses') with the same technologies.
- Anamorphic lenses... They should exist. They complicate lens production because a stable quality (for series) of an aspherical lens can be achieved only from a central part of a large glass.
- Focusing is the process that often requires a separate person (focus puller) and additional machinery (follow focus system). All cine lenses have exactly the same standard focus wheel. There is no such standard for a photo lens focus wheel.
Nikon F has very few cine lenses and has no series of lenses. Nikon Z has nothing. Thanks to the closed very secret, unique, perfect, bla-bla specification of Z mount and zero collaborations with other manufactures.