Electrifying a line isn't as easy as simply pulling a cable. You need more space above the train for the power line, which means all bridges and tunnels have t

Electrifying a line isn't as easy as simply pulling a cable. You need more space above the train for the power line, which means all bridges and tunnels have to be adapted, thus rebuilt. You need space in the side to place the masts, which may mean acquiring land or some complex engineering in close (hilly?) areas. This then often means that regulation treats it as a major change, thus the whole signaling system and other aspects have to be adapted to current standards. And then you need all the side infrastructure like substations etc. In the end it's almost as expensive as building a new line.