There are 2 points: first is trains come upto Rae bareily then switch to the shorter rural line and merge at Unnao thus bypassing Lucknow. I think IR ought to do it for some weekly trains but LKO is such a big station that except for dedicated passengers, no train does it.
Second and what still baffles me, is the Kanpur-Unnao-Allahabad line. This line is not much longer than the main line and while the mps is ~110 only it bypasses much of the congestion. Only a passenger, ICE and one Express...
more... runs on it. At night, it resembles a ghost area. Most trains just go straight from Kanpur to Allahabad without stopping at Fatehpur [the only major station enroute NCR], so they can in theory, be done via Kanpur-Unnao-ALD route as well. Especially for trains that end at ALD, there is every reason to use that line. IMO, the ALD Humsafar should use that line for once. It starts from there only, so it can easily be shifted to 'Prayagraj Sangam' if needed and started [and it is basically non stop till Delhi except for a Technical halt].
All IR needs to do is upgrade these lines to consistent 110+ mps and proper double them at all places.