Honestly, I think they should include the game, but do what some companies do, just sell it directly from their site.
I can chime in here. There's a couple reasons for why the game isn't included.
1) The Panzerhund Edition is only sold at store.bethsoft.com and It's limited to 5,000 editions
worldwide. Logistically we have no way to anticipate which versions people will need (NTSB, PAL, etc.)
2) With many people purchasing the game digitally, we wanted to provide an option to purchase the content without needing to purchase the disc.
3) We knew many folks had already pre-ordered to get into the DOOM beta.
Worth noting, if you already pre-ordered a physical copy of the game already, it includes a steelbook case you can put the game in.