The numbers are just far lower then cars. The individual parts are far larger and far lower numbers. You can't have as much economics of scale. Also, every cus

The numbers are just far lower then cars. The individual parts are far larger and far lower numbers. You can't have as much economics of scale. Also, every customer has a lot of wishes. Imagine it more like Uber buying 1 million GM cars demanding to have costume interior and many other details. It really depends on what the train is supposed to do. A train is mostly costume to its mission. An S-Bahn that operates more like metro, needs lots of large doors with a open layout. The same basic train can also be configured for an inter-city operations, having very different layout, different doors and so on. And each country has different standard, differ track gauge, loading gauge, signaling, breaking and so on. Accessibility standards is another huge thing that is slight different everywhere. But even so, lots of train types are quite similar, lots of train are built on the same platforms. Each of the manufactures have a few standard platforms. And inside different train there is lots of reuse.