It's a tragedy of the commons situation - you might be able to buy 90% of the land for a "reasonable price" (which is hard to define - depending on the type of land use, the value of the owner's entire plot would change significantly by having a train going by every day, sometimes greater sometimes lesser), but if the remaining 10% don't play ball you can't have the train.

So the government is in a position of "we'll give you X for this, but if you don't agree we'll just take it from you", which is a... non-Texan position for government to be in, to say the least.