There are no technical issues, but the main reason is speed. LHB coaches were procured for the sake of having high speed rakes. A part of this comes from the better suspension, and the other part comes from the lighter weight of the coaches. Adding self-generating equipment automatically increases the weight of the coach and also increases the stress on the tracks. This will limit the MPS (for comfortable travel) to 110-130 kmph and also increase maintenance costs. This is the reason IR is moving towards HOG now.
However, the increased speed and other features come at a price. With self-generating coaches, it is very easy to rearrange rakes, provide slip coaches, adding extra coaches etc whereas with...
more... non SG coaches, rake integrity must be maintained very carefully. But if 150-160kmph are the targeted speeds for trains, then SG coaches cannot be used.