If I had a few billion for a TSMC factory, I would...

This is what I'm referencing. The memory sits on the package with the processor, connected with thousands of microscopic traces, so fine it needs an expensive substrate rather than a typical PCB, and expensive equipment to assemble:

The connectors are tiny, and made with immense precision. There are about a thousand reasons you can't just transfer HBM once its been used, and besides; other memory controllers wouldnt' support it.