I'm sure there are other complexities added in when there are pieces of iron rather than silicon involved... and safety regulations start chewing up time and reworks.

But overall, the "if it is possible to do, but someone put too low of a cost in the budget or tried to get it done faster than the engineers said it was doable"... well, isn't that bad project management that promised too much and underdelivered... and then got a canceled project? Is there something else it could be?