cubemapってbspのファイル名を変えると機能しなくなっちゃうんだ
https://developer.valvesoftware.com/wiki/Cubemaps
If the map bsp file is renamed after the cubemaps have been built the cubemaps will no longer work and default to the sky cubemap. You must rebuild cubemaps again each time a map is renamed. However, the no-longer-working cubemaps are not removed, so this can lead to bloated files. If you plan to release a map so that others can download it, it is best to try to avoid any map-renaming after you compile it, to avoid problems.