Although it sounds a waste - if they had managed to rescue the crew, the cost of retrieving the marooned orbiter, along with the risk involved, would probably have added up to a waste of money. Launches were costing $500 million each. Add on the cost of developing a retrieval mission, with (as described) very detailed and difficult planning. The mission would need to work out how to repair the orbiter in space, bring the systems back up, which would probably involve procedures that were never intended to happen except on the ground with specialised equipment. You could easily spend another $500 million. And you have a very real risk the orbiter fails and kills everyone onboard anyway. A second hand orbiter just isn’t worth it.
The story of the Columbia accident makes for worthwhile reading. There were lots of issues. But the creep of acceptable failures was at the core of it. NASA got away with a failure that the original mission rules dictated was a mandatory grounding of he fleet until solved. But since they had been getting away with it, they continued to launch, even when it was listed as a critical failure that needed solving. There were contributing issues. The RCC sections degraded over time. The leading edge sections on Columbia had done a lot of missions, and when they tested a new section versus one with a similar number of missions taken from another orbiter the difference in strength was startling. A foam block of the same size and composition hitting the new section at the speed the one hit Columbia’s wind left minimal damage on the new section, and punch a hole big enough to crawl into in the old section. Part of the degradation turned out to be dissolved zinc in the rainwater runnoff leached from the launch structure anti-corrosion coatings. But the number of missions and re-entry cycles was the big contributor.
The investigation uncovered other failures, for instance the explosive bolts that held the top of the SRB to the stack were supposed to be captured in a cup when separation occurred. There were failures of the capture device, and bolt fragments were hurled through the air near the orbiter. For a while this was a credible alternative to foam damage.
What really caused the accident was a systemic failure of safety culture at NASA. The facility building the external tanks had reduced staff numbers. Things like the person responsible for safety oversight was also the guy that signed off on completion. And there were monetary incentives for on-time completion. You can see where this goes…