the material being raised and lowered must be very cheap (to be able to afford much of it)
the material must be possible to automatically handle in arbitrary amounts
the friction of raising / lowering the material must be low
the handling should not require a slope of particular grade or a specific height
Trains fail the cheapness and arbitrary amount check, along with the slope grade check. Sand fails the friction check. Concrete blocks are close to failing the cheapness and arbitrary amount check. Cranes fail the specific height check for certain ranges of height.
Water... it also requires a certain slope grade, but the range is not narrow.
Yep. As for why:
Trains fail the cheapness and arbitrary amount check, along with the slope grade check. Sand fails the friction check. Concrete blocks are close to failing the cheapness and arbitrary amount check. Cranes fail the specific height check for certain ranges of height.
Water... it also requires a certain slope grade, but the range is not narrow.