It's true that any rotary wing aircraft has limited speed, but the Rotodyne was exceptionally fast in its day, I think 190 knots. The V22 is almost twice as fast, but also has speed limitations and noise/fuel issues due to the large size of its propellers. It also has no forward-firing gun so it is very vulnerable in close support ops/Marines use.
But speed is only one aspect of any craft's capabilities, and it is not necessarily important for lots of situations, like shortish flights (City to City), military use, and activities in remote regions: mining, forestry/logging/firefighting, medical/food/drought/flood, as well as special events like getting people to festivals and sporting events. The Rotodyne concept allows VTOL, safe transition to forward flight similar to autogyros or helicopters plus a much better degree of safety in the event of engine failure. With sufficient fuel it can also hover.
Certainly it would serve in niche markets rather than mass transport, but these niche markets exist and can be profitable