I'm sure those responding to you will not 'shoot at you' as happens on other threads (US taxpayers are not footing the bill for this aircraft). In general easy answers to your question as using jet engines have associated characteristics and design efficiency levels as well as safety issues that would not allow it to be a viable choice for the intended capabilities of a commercial tiltrotor. (and of course using pure jet engines would make it a "TiltJet" rather than a "TiltRotor").
