Typically because Arri, Panavision and Sony are more rugged, easier to rig, do not overheat and are the cameras that DPs, Directors and Producers like/trust.
We will see if Blackmagic Design’s 17k 65mm, 12k Cine full frame and Pyxis 6k full frame have any impact on that.
Don't tell Alex Lindsay that. 😄 I remember years ago he wouldn't shut up about RED cameras. Granted things may have changed over the years, I stopped listening to MacBreak Weekly almost 4-5 years ago now. The way he was talking back then all other manufacturers might as well just go out of business.