Too many remote locations where no wires exist...
If that was true, you wouldn't be planning to put cameras there.
Every camera is physically wired to power, and you can usually use the same power lines for network data. Search for powerline networking adapters.
Note that powerline networking is not perfect. It has a lot of limitations similar to a WiFi system. A lot of factors, like the noise levels generated by other devices plugged in to power, will reduce speed. Another problem for some people is when they have more than one breaker box they find the signal can't go from one to the other. My "500 Mbps" kit only achieved 40 Mbps actual speed in my home with only one breaker box. Still is better than WiFi, though!
Remember everything on WiFi is a source of interference for everything else on WiFi. The fewer devices you have using it, the better. Analog cameras like x10 are actually worse than WiFi IP cameras in this regard. They use the same 2.4ghz radio frequencies, but they are analog so they typically use a huge piece of the available radio spectrum and they transmit 100% of the time
without ever stopping. Just one or two analog wireless cameras can make WiFi unusable in the area. The same can happen with WiFi cameras, too, but it usually takes more cameras to render a system completely unusable.
