For smaller high density countries i would agree yes. For larger more spread out countries high-speed rail systems(assuming your referring to maglev) are simply to expensive at the current time.
I have no idea what you are referring to by tubes though.
> I have no idea what you are referring to by tubes though.
Probably a reference to Elon Musk's recent claim that he had come up with some secret technology that could dramatically improve long distance transportation, with much (much) higher speed, lower energy usage, and (much) lower cost than conventional HSR.
Unfortunately the only detail Musk would give was a very hand-wavy reference to "tubes," and a subsequent clarification that he didn't mean the usual sort of "evacuated tube transport" people have talked about for ages and ages.
Based on all the discussion I've seen, though, it seems pretty likely it's just a vague idea Musk had that he didn't bother to think through, and it will fall apart when he tries to fill in the details...
You're assuming the network has to cover the whole of the low-density country. The United States is an overall low-density country with high-density regions within it. The average density is pushed down by huge swaths of effectively empty territory between those regions.
Using HSR to facilitate movement within the high-density regions can make sense, even if using it to facilitate movement from one high-density region to another doesn't.
Unfortunately I do not find the link, but there was the proposal to build (at least partially) evacuated tunnels between cities. This would reduce air drag and therefore energy consumed, particularly at high speeds. ( This is of course 1950 SF tech.)
I have no idea what you are referring to by tubes though.