Whilst flat-bar "road bikes" may be rare, flat-bar touring bikes have a long history. These are usually custom builds, but have a trad lightweight touring frame with city bars (rather than the straight MTB flats). A friend of mine has one in Reynolds 531 c, with shimano nexus.

Some people prefer flat bars with a more upright riding position, but you can use them just as well down lower. In France they commonly come with randonee bars, ie drop bars without the drops.

Compared to a hybrid, they have a lower bottom bracket, and lighter weight.

I think giving these bikes their own name is a bit of marketing hype.