The main reason is that multirotors are a much more recent solution, and they started as small unmanned vehicles because the regulation is much simpler (the req

The main reason is that multirotors are a much more recent solution, and they started as small unmanned vehicles because the regulation is much simpler (the requirements for airworthiness certification for multirotors are not standardized yet). But I believe that we will see more and more applications for multirotors in the future. As a concept, they are safer than helicopters, with much simpler mechanics.