this ebuild should be depends to media-libs/libtxc_dxt, else it cause alot of problem f.e: http://steamcommunity.com/app/221410/discussions/0/864959336401282074/ Reproducible: Always
It does not depend on this package as it is not required for everyone. Steam-meta depends on steam-games-meta which depends on media-libs/libtxc_dxtn if you activate the use flag for a mesa-based driver and a game/engine that needs it.
thanks u very much for this information, so it solved