Trains aren’t traveling at 400-700 mph ground speed. At best they might be doing 225mph. The rate you pass by towers is thus lower. Trains also have trees, hil

Trains aren’t traveling at 400-700 mph ground speed. At best they might be doing 225mph. The rate you pass by towers is thus lower. Trains also have trees, hills, buildings, earth curvature, etc obstructing how many towers your phone can see. Planes generally have a clear LOS to the tower over a significantly larger area because of the altitude. If the radiation pattern of the tower wasn’t the shape that it is, the problem would be even worse in fact.