LOL. French here. I am not sure where you get that impression, but TGV lines cost dozens of billions of euros to be built, and the ROI is calculated in 30-40 years time, so saying the "TGV is highly profitable" is a pure lie, because we don't know in 40 years if people will still take it as much as now. On top of that, the SNCF (public company operating the TGV) is a sponge debt and if it were not for the ongoing government spending to keep it alive every single year with huge cash injections, it would have disappeared long ago.
Yeah "highly profitable", hey.