I didn't say luxurious, I said lacking in basic amenities. You're absolutely right that trains should be for everyone, not just for the rich -- but everyone also deserves to travel with a certain basic level of sanitation and comfort that isn't there on a lot of Indian trains. Just because they're cheap doesn't mean they should be shit.
The toilets are filthy and unhygienic, the running water often...isn't, the bed linen has been found to be dirty and/or infested with vermin on quite a few occasions, and the general state of most trains is just bad. Over and above that, the trains themselves haven't been upgraded in years AND an increasing number of them just...aren't in service any more, which means delays, horrible overcrowding, conflict on board the train, and an overall unpleasant passenger experience that further drives people away from taking trains.
This is made a lot worse by the fact that the railway authorities here tend to focus on trying to improve the experience for actual rich people in the upper classes (ie. 1st class/AC class) who aren't even taking the train anyway -- they're flying. That means ticket prices for even the lower classes are rising, because all that money has to come from somewhere, but there's no commensurate increase in the standard of service.