Why was the Bell Boeing V-22 Osprey not worked on more?
The Osprey has arguably been quite successful considering the circumstances. As Energizer777 points out, the basic idea is not new, and there were many engineering challenges to create a viable aircraft. That these challenges were solved and the plane is now in production and active service seems to be a pretty big success. Also, this has all happened relatively recently. The V-22 first flew in 1989 while the F-15 and F-16 both date back to the early 1970's (and are still in active service). The challenges in refining the design pushed introduction of the V-22 out until 2007. The design just hasn't had enough time to mature past the first successful application. You might consider the civilian tilt-rotor AW609, currently targeted for certification in 2017, as the next advancement of the design.

Props/rotors are more efficient than a jet engine at low speeds. Given that the slow and vertical portions of the flight are very important to the design, this decision makes sense. The prop wash also flows over the wing, allowing the wing to be more effective with a short span. Using turboshaft engines rather than jets also allows one engine to drive both rotors if the other engine fails, making single engine operation easier.

You are right about the drawbacks of the design. The V-22 is noisy and not as agile has a helicopter in slow flight. Maintenance requirements are high and were certainly an issue early on in the introduction to service. And upfront costs are also more than a helicopter or airplane of comparable size. However, the capabilities you listed first are worth these added costs, at least to those that have purchased/ordered the V-22.