In Europe you have an extensive electrified passenger network that’s easy to supply with electrical facilities due to a general lack of remote areas.

Many rail networks in the world have these areas where it is incredibly expensive to install electricity and they also don’t have the privilege of having invested in electrification for a century. There’s really not a good way to just electrify part of a network if mainlines are going through areas where electrical rolling stock can’t/won’t be served.