Out of curiosity: Why some vanilla texture folders aren't in the game

[MysticNaz99]

What I mean it's that when I was looking for textures in the zone builder I noticed there are some texture/flats folder with textures that don't seem to be in the actual game (e.g. Acid Plant, Dark City, Honeyhive, etc), so I wan't to know why they are in the game's files

 

[romineblox0]

you can use these for your own maps