I think population density is a factor. China and the US have the same area, but China has 4x the population. Consider also England and Japan, densely populated islands with great train service.
I define great as it being generally possible to get where I want to go on the train (this is the most important factor) and then as a bonus it's usually competitive with driving, busing, flying, cycling, or walking in terms of comfort, cost, and convenience.
When people praise train travel it is largely long distance.
When people complain it is likely to be commuter lines in and around cities.
BTW, TGV is French...