Interesting videos
What a lot of people are not aware of is that transformers contain mineral oil, a lot of it, which is one reason why fewer tie-downs and only anti-slip techniques are used, government, electrical companies and the the railways, would much prefer the transformer to roll down a hill in one piece that to have it split open and 10,000 gallons of mineral go into the local water supply.
Plus to restrain that kind of weight your talking chains that would need to be so thick it would be impossible to lift without a crane and adding another 5-10 tons, so it's impractical, also can you imagine a transformer still attached to the flat car derailing, the damage would be huge and again expensive.
The bow in the flat car is obviously from the weight, which is as it should be, the flat car has to be able to flex to accommodate uneven track, curves, crossings and so forth, if you look at any fully laden 18-wheeler you'll see the trailer also has a slight bow in it. If it were rigid after a while you would have to replace the entire trailer or flatcar as the chassis would weaken and snap, if that were to happen on a railcar at 30mph with say10-15 cars behind it, (and those cars could contain anything), so another possible environmental and definitely expensive cleanup.