Because main thing is tracks and not trainsets. We had Wap5 in 2000 and LHB in 2003. Wap 5 and WDP4 are capable of 180kph in trials and 160kph in commercial runs( for Wap5). So trainset-wise we were capable of going at 160kph in 2003 itself. But problem was tracks. Still now we have the same tracks, no upgrade. We can build trainsets which go at 180 or 220 kph but they run on tracks, not on thin air. Unless tracks and sleepers are replaced it is difficult to expect speed increase. Forget 150, even 130 is possible only on HWH-NDLS and NDLS-BCT which is only 5% of the tracks.