I haven't actually played any of these, but I suspect this might be related to "RandMap" usage. On the Mattm Randmap page, it says the maps were made by Randmap, a tool that generates maps randomly using predefined themes and prefabs.
RandMap supports "random generation of rooms with 30 different basic types of rooms, each type with numerous variation of dimensions created algorithmically. Automatically creates .map file, runs QCSG, QB RandMap is a program that creates random maps for the Half-Life. At the moment is supports Half-Life single player and the SvenCoop modification, which is a modification whereby players can play Half-Life cooperatively."
The output from this tool all probably looks similar. Entire rooms and areas are basically identical.