It wasn't just textures they used to show how unsafe Black Mesa was. Many things throughout the game suggest the actual state of the facility. E.g The equipment was being used for things it wasn't intended for, chemical spills, few ways out (One of the scientists says opening the Silo doors is their only way out), poorly maintained areas that will still in use etc.
The lack of things such as doors or safety railings wasn't just due to technical or gameplay reasons.
I don't see what chemical spills and the equipment (the first being used in a non-accessible area to showcase the state of the place and the rest only being when it directly affected the players progress) has to do with the hilariously few amount of doors that are in Half-Life there aren't intended to be used by the player, or rooms where sense has been compromised for a certain gameplay feature. Most of the detailing was still done through texturing the level geometry to detail it, instead of having actual 3D details.
I promise you that if Valve had made the game today, there would have been doors everywhere, because not only are they a good way to spice up the surroundings, but also to make an area seem much larger than it is by having places inaccessible to the player.