The branding of trains in democratic setup like India is to differentiate and also highlight during the elections. This is the same for all the government's and railway ministers (some times) promoting their parties or image.
Indian railways could not able to merge all the similar category trains into a generic name.
(1)...
more... As we discussed earlier, the type of trains like Duronto, Humsafar, Gareeb Rath, SK, Rajdhani, Tejas Rajdhani, Vande Bharat Sleeper, etc are one category - "AC Superfast" trains.
(2) we can take all long distance trains like Mail, Express, Antyodaya, Vivek, etc as "Express" Trains with commuting average speed of less than 60 kmph.
(3) Trains in SuperFast category can continue as "Super Fast" trains with minimum 60 kmph average speeds
(4) Shatabdhi, Vande Bharat, Gatiman, Etc are in "AC Intercity" trains.
(5) Jan shatabdhi, Intercity, Vande Metro, Double Decker, etc in the " Intercity " Trains category.
(6) All passenger trains, MEMU, DEMUs, etc can be combined into one category "Janata Express".
(7) All local trains will continue as "Suburban" trains.
These categories will reduce the confusion and also streamline ticket prices across the current nomenclature and avoid confusion amongst ticketing staff in issuing the tickets.