This was discussed before. Modern subsonic engines are an engineering marvel because each successive generation has to save even more fuel and go longer between overhaul. It's getting harder to squeeze a few more percent out.

Supersonic engines on the other hand haven't seen as much development in those directions. The major engine manufacturers passed for the same reasons Boeing and Airbus did on a SST. It cannibalizes their existing product lines and is a moon shot level pipe dream.
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Successful pipe dreams are what Schumpterian creative destruction is all about. Many will try and most will fail but occasionally an upstart will come in and change everything because the dinosaurs at the top of the industry had no incentive to do so.