Cab signals are (usually) transmitted through the rail and picked up by a special receiver on the leading axle of the locomotive. Each locomotive has to be equipped and the rails themselves have to be checked and blocked. This also means the rails have a higher maintenance requirement as opposed to lineside signals which can be more easily maintained.
However, some countries (Brazil predominantly) have embraced a GPS based cab signal system where lineside signals are almost totally eliminated. However, this was done with federal subsidies to cover the expense iirc.
Another example is the US Northeast Corridor where cab signals are used along with lineside signals to provide a level of redundancy at speed.
Unfortunately there’s no easy solution, but I lean towards the Brazilian GPS based systems from Wabtec.