The Concorde was given — for free — to BA and AF by the consortium (BAC and Aérospatiale) of government-backed companies that built it.

And this was back when both of those airlines were majority owned by their respective national governments (they were later privatized).

The plane was built by government-backed companies with huge government subsides and then given to airlines which at that time were subsidized by the taxpayers. That’s how they could “make it work”