Reading a few articles about this, it seems a big concern is area. They wanna squeeze them in every free space they have between and around roads. Conveyor belts can probably do a lot sharper curves etc. than railways. If they do special small rails, they’ll also need special trains for that.

From the articles it’s also not clear if it’s from one point to another point or from multiple to multiple. They talk about deliveries, which would rather be multi to multi, but it’s not explicitly mentioned anywhere.