It is FAR more than cameras. The "broadcast facilities" for sporting events are the trucks you see parked outside that contain all the control stuff, and uplink to the network's main site. Those facilities aren't built into a stadium, because the equipment ESPN uses is different from Fox's, which is different from CBS's etc. so the network has to bring a lot of their own.
The 4K production trucks are completely different, all new equipment. They aren't building a fleet of those, the networks have only or two right now. Then they have to have enough transponder space to uplink 4K from the event to the network, and then from the network to all the headends for Directv, cable etc. Some of them may be on broadband now but it will be many years before they are ALL on broadband and they can do away with the satellite uplinks, so that is a limiting factor.
I'm sure Kyl416 could come up with another dozen reasons I haven't thought of...