Very long distance trains like TN, GT, Kerala express etc have a very large number of UR passengers depending on them. As all of these trains are already 24 coachers, conversion to LHB will cause severe inconvenience to the UR passengers. For over-night trains and short distance trains, buses and other cheap options are available and are comfortable also. A UR passenger who can't get a seat in MAS-MAQ can find a good number of buses or a convenient chain and travel relatively easily. But a UR passenger between Delhi and Madras will be literally stranded if he can't find a seat in the train.
For this reason, long distance trains, especially those that are already 24...
more... coachers, should not be converted to LHB unless the CC can be increased. However, shorter trains like TNSK, NDLS-PDY etc can be LHBfied first as conversion will not impact CC for these trains.