It has very steep cliffs and it's very narrow. It's the only main road between the two small towns.
I can understand the locals annoyance when they're stuck behind a cyclist for the whole stretch and cannot safely get around them without risking their life or the life of others.
There are plenty of roads in the area that are safer, not to mention the abundance of off road riding trails for mountain bikers in the area.
Cyclists deaths is misinformation, but the sentiment from the locals is real and warranted: please choose another road, this is our only road and we got places to be.