They actually use road bikes for these, though they're versions that are now called "endurance bikes". They're a pretty popular segment of road bike sales now. The two biggest models are the Specialized Roubaix (named after the race of course), and the Trek Domane. Both are basically road bikes with relaxed geometry and some compliance features to reduce/absorb vibration so the rider doesn't get tired as quickly. And of course wider tires, typically 28 or 32mm, but this has actually become the norm these days for road bikes anyway. (23mm tires used to be the norm, but that's gone out of fashion now, as people have decided you don't gain enough in efficiency with such skinny tires to make the downsides (punishing ride quality) worth it.)