Why should downloadable games be different from physical media games? Both are the essentially the same bits and bytes. Why does it matter whether the bits in question are delivered via sneakernet or internet?

Enabling resale of digital goods has very high risk of crashing the market, as they almost by definition do not degrade in use. Historically the second hand markets have been limited by local availability, but internet removes such barriers for digital goods and that makes the situation very different for games compared to conventional items such as books.