I second waflija’s opinion, and this is especially visible playing on high difficulty level. Intercity tram lines (together with truck lines) are the only way to make a good profit at least from 1850 until 1900, and even after 1900, trams are always a better solution for short/medium distance lines between cities.
Only longer lines become profitable by trains, but due to the limited map size (at maximum size too), it’s extremely difficult to have more than 2 long train lines on any map.
As already said, too high loading/unloading times of trains, lack of very small train stations and too high maintenance costs for trains, together with some other factor, all contribute to decrease the train lines appeal versus tram lines in the limited size maps of the game…