Why no trains and planes in My Maps ?

Question

in Google Maps I can select itineraries by plane or train between A and B, but when creating my own map in My Maps, I can only select the 3 others transport means (car, bike, walk)
Why ?

barryhunter · Accepted Answer

In general, public transport navigation needs a specific date/time. But even if was able select a date, the routing is subject to change over time. 
Would need a specific way to 'update' the routing, which would change the map display. 
Ok, technically road/walking navigation can change too, but at a lot slower rate.