(Note that Fallout London is a fan-mod, not an official new fallout game)
Any game as old as FO4 is going to have huge mods (and probably most small mods) that require all the DLC.
That’s how it’s been since expansions and mods have both been things. Literally “welcome to PC gaming”.
Expansions/DLCs will usually have game fixes inherently included.
Even if they don’t actually “use” the DLCs, it makes sense to require the same content that the developer owns and used to test the mod.