In both Factorio and Satisfactory I end up using long (and I mean, multi-kilometers-long) belts all the time and never trains.

Something about the track building being clunky, or I don't know what really the underlying thing that's making me prefer the simplicity of items-moving-and-splitting-and-merging-on-belts is

You should give them a shot again with 2.0, they made a ton of improvements to the track building:

https://factorio.com/blog/post/fff-377, https://factorio.com/blog/post/fff-389, https://factorio.com/blog/post/fff-403