It's a time-arbitrage problem: there's no one else producing it (thus no free market) so they get to charge literally whatever they want since they're the only manufacturers, for as long as it takes a competitor to build another competing production line. This is reprehensible.

Once competition returns, the price drops again, and no one makes ludicrous profits anymore. But if the expected returns in competitive conditions are miniscule, there may not be sufficient incentive to produce a competitive market for this individual drug again.