It's difficult as it will be a circular route not popular among end to end people.
And Railway avoids bringing new trains on a not-direct straight routes.
As far as Mumbai Howrah Mail is concerned, it is one the most old trains of indian history and was introduced when Bombay Jabbalpore line and Delhi Howrah was joined at Naini to connect Mumbai with Howrah in the preindependence era of railways as there was no other route connected then from Bombay Victoria terminus to Howrah.
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to this historical importance, railway which would have otherwise shortterminated this train into Howrah Patna etc and or diverted this via Shorter route, is not doing so.
I think, earlier it used to run via mgs pnbe line before commencing of mgs Gaya hwh line, after which it used to run six days via this shorter route and one day via pnbe.
But in 2006-2008 around, a new train via pnbe was introduced Mumbai Asansol express and this Mail was made full seven days via mgs gaya.
This Mail was the regular news articles topic in Ald and nearby area, when it was diverted via ACOI and was opposed by many historians in the city.

Upper India should be shortterminated at bgp or mldt in East end and Lucknow or Varanasi in West end
No use of so long route train from Delhi to Howrah via lko, BSB, mgs, pnbe, bgp, bhw, Kna, hwh
Also, ltt ghy should be stopped
And two trains weekly Humsafar from bgp to LTT and weekly superfast from bgp to ghy be started in...
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that place