That bus is only useful for one origin/destination pair: WOR and NYP. It doesn't serve Boston to/from Worcester, Palmer, Springfield, Hartford, New Haven, Bridgeport, Stamford, and intermediate stops. It doesn't serve Framingham to/from Palmer, Springfield, Hartford, New Haven, Bridgeport, Stamford, and intermediate stops. It doesn't serve Worcester to/from Palmer, Springfield, Hartford, New Haven, Bridgeport, Stamford, and intermediate stops. It doesn't serve Palmer to/from Springfield, Hartford, New Haven, Bridgeport, Stamford, and intermediate stops. Etc, etc, etc.
If the bus did try to serve all those points, it would get stuck in traffic in every city center, and it would take far longer than the train. That's the value of the Inland Regional: it can efficiently serve many well-located stations on a single trip, which an intercity bus cannot. It can do so with a reasonably high degree of schedule reliability, and reasonably similar travel times at all hours, which an intercity bus cannot.
In order to have intercity buses match the usefulness of a single Inland Regional train, you'd have to run a fleet of buses with different stopping patterns - and you'd almost certainly have forced transfers with long waits for late connecting buses for many O/D pairs.