This is odd to me but I guess the travel times by road are sufficiently short that they don't feel the need to have the additional transit option. Something that the video I linked to made me realize is for the long-distance Amtrak lines (which they are toying with cutting), those routes are the only public transit link to the outside world for far-flung villages and hamlets. Ridership isn't high because the towns themselves are small but for anyone who doesn't have a car or can't make ~5-10 hour drives to go anywhere, the train is a great option.
Or maybe the hyperloop route would not have stations at those towns so they'd get no benefit? I can't imagine hyperloop being run efficiently and quickly if it has to stop every 5 miles / 7.5 km.
On profitability (your Amtrak lines):
There is in Groningen a normal rail network that together with public busses connect most villages.
The loss of roughly 50% on operating is paid by the government.
It is imo not possible to have a somewhat adequate public transport in the rural provinces in NL that would break even.
If I say it more blunt in general: all our rural provinces are lossmakers subsidised by the urban areas (All farmers and on top a lot by salaries of civil services, social securities, education and health care salaries). Many initiatives during especially the 50ies and 60ies in the 20th century to counter this with generous public capital investments and subsidising companies have in effect failed.
But because this subsidising was done our income inequality in NL is not that big.
The best long term way forward I see is to concentrate the working population along a few logistic connections and convert the rest into national parks, forests, lakes, bog areas with eco-farms in them with on top some holiday resorts, welness centres and pensioneers.
That 3 km tube in Groningen would only be for testing for R&D
The objective is to draft an Amsterdam - Frankfurt connection of 450 km, connecting two big intercontinental airports, which are also hubs for continental flights and other mass transportations.
National plans in NL include a high speed train between the city Groningen and Amsterdam (200 km) but I doubt that will ever become a tube. Most money the coming 20 years or so will anyway go to light rail connecting the bigger cities in Holland (Amsterdam-Utrecht-Rotterdam-The Hague and the urbanisation areas in between those cities along the existing rail and motorways. Together a dense crescent moon around a big green polder that should stay green).
New residential areas for our population growth, mainly from migrants, to be build along that light rail and NOT in existing green and rural areas. Densification.
The reason to build that test tube in rural Groningen is space (also at low cost)
And the Provincial authorities happy with any activity that increases economy with higher value jobs.
