The zonal railways don't really have any influence over the RB. But the state government can lobby for it. But no politician in AP is fighting for such useful projects. And the BJP government too is now hell bent on winning over the people, so they are more worried about getting the credit for sanctioning projects. They will wait till elections to make any announcements.
That's partly the reason why SCR hastened the doubling/electrification of GNT-GTL section (which was given the go ahead earlier) as that route now carries most of the freight traffic that should ideally go through the KRNT route and that is readily visible to the RB.
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more... The presence of KCG at one end also discourages freight movement on the route due to the heavy passenger traffic. So, RB is more interested in doubling the freight-heavy route over the passenger route.