You might think it is is inefficient to have a miracle cure for cancer tied up on patent for 20 years, but what are you comparing it to.
A rational company would lower the price if that broadened the market and netted more profit by volume. Drugs aren't Veblen goods.
The impetus for jacking up drug prices is that the market is captive, and those who need the drug will obtain it. That and insurance/government is often the payor.
It's the same reason SAAS took off so much. If you sell the product and consumers are (relatively) happy, now what? They might come back and buy another version in 5-10 years, but how do you generate enough cash flow between now and then to stay afloat?
The time value of money means you want to sell every dose as soon as possible. with a 10% annual return, $1,000 today is better than $2,600 in 10 years.
Additionally, each day that passes, someone else can come in and outperform you or undercut your price.