It used to be more common to have optional texture packs like this. It seems to have fallen out of favor, I can offer some informed speculation as to the reasons:

* Every additional configuration i.e. 'texture pack vs no texture pack' is more QA workload to verify that everything works as expected. So adding this option is more work for your already-busy testers.

* Adding DLCs to deployment systems like Steam or PSN is additional work and then when patching the game you would also need to patch the DLC. I can imagine the coordination overhead here being a pain.

* Some users will fail to install the DLC and then complain that the game is ugly or that the screenshots were misleading. This is ultimately a user education problem but it's also the case that the flow for installing DLC on most platforms is awkward.

* The DLC install process adds additional points of failure, so you need to handle all of that now too.

* Users installing a new graphics card will probably be annoyed to have to suddenly wait for a HD texture pack to download before they can test it out.

All pretty minor individually, but it probably adds up to explain why most studios don't do this.

I wonder how widespread developer support for Xbox Smart Delivery (which is basically what you describe) actually is at this point?