Umm and who offers such option, buy physical and get digital for free? Sony? Microsoft?
Not to mention that offering this will allow you to buy game, install digital, sell cart and get your money back.
You know, the only reason game companies don't do this is pure greed. These days it's staple for other media (movies/music) to include digital copies when you buy physical. Hell you buy a UHD Blu-Ray and you get the DVD, The UHD Blu-ray and an "Ultraviolet" digital copy to install on up to 3 devices. IMO they definitely should offer the same for games. We shouldn't have to buy it twice to own physical and play digital.