I really don’t understand that argument. So is most of the US not connected to the sewers? Since these are also dug underground. If you already dig trenches for the sewer system, then you can also place electricity lines for relatively cheap. Though that was not done in the US and retrofitting is a big cost, usually only done, when you need to dig either way (e.g. for modernizing the sewer system). So its more about the default and if a country can take the opportunity when sewers get modernized

Though in development of an area you probably already dig up the ground for other utilities, so in that case it is relatively easy and cheap to also put electricity lines in there too. But retrofitting in an already developed area is really expensive. So it becomes more a question of the default.