The vast majority of water that goes down a shower drain is pretty clean. While you're rinsing off, the soapy water going down the drain is also getting diluted, until it is pretty clean. A shower drain is not much different than your kitchen sink, or the vanity sink, or any other in the house. A foot to the trap is still within limits, but I prefer it to be closer to the shower pan. The walls of the drain pipe do tend to get scoured from the running water, so there's not much to eventually smell. If it does, it's not all that hard on most showers to remove the grate and use a bottle brush to clean things. Even on a vanity sink, most have an overflow, and even if you close the stopper, you can get some smells from the walls and overflow area...IOW, a stopper won't help. If the plumbing is not done right, the trap can get siphoned dry, and that CAN make things stink, as you then have an open pipe directly into the sewer. A fixture rarely used may need you to dump some water into it occasionally to reprime the trap. When I go to my mother's house, the fixtures upstairs (that almost never get used unless someone visits) are often dried out - the toilet has almost no water in the bowl, and the shower and sink may be dry. All it takes is one use, and they're back to normal for months again, at least most of the year.
FWIW, there are lots of things in a shower that can smell, especially if it is not built properly. The drain is not the usual suspect.