1. University/startup company finds a promising drug candidate that works in-vitro. They make a press-release, researchers write their theses, and move on.
2. Drug companies pick that up and run small-scale tests. These tests are negative, usually because of unexpected toxicity.
Looking at the molecule in question, it's likely what happened here. It's a covalent inhibitor, meaning that it permanently binds with the protein. It's also allosteric, meaning that it binds to the target enzyme but not at the actual active site. This is a huge red flag for toxicity, because it's likely going to bind to other proteins that can have similar configurations.
3. But the underlying idea is sound, so companies keep working on alternative approaches. They are likely looking for non-covalent compounds now, or for things like "suicide inhibitors".
4. You'll see actual trials in 10-15 years after the initial press-release. Most likely for completely different compounds, targeting the same mechanism.