why the investors are drinking the coolade investing in AI debt ..?

Because they.are spoiled with returns in technology and other markets which are driven due low interest rates in last 20+ years .. going forward rates will stay high and the funds invested at these rates may not be as lucrative as in past 20 years.

Moreover, a good chuck of the debt is funded by private equity which always chases new stuff.. remember the term venture debt used during late dot com period by companies like WebVan.com