I have never heard of any company, no matter how big and experienced, where it is possible to decide that an ASIC design is valid by any other means except by paying for a set of masks to be made and for some prototypes to be manufactured, then tested in the lab.

This validation costs millions, which is why it is hard to enter this field, even as a fabless designer.

Many design errors are not caught even during hardware testing, but only after mass production, like the ugly MONITOR/MWAIT bug of Intel Lunar Lake.

Randomly-generated HDL code, even if it does not have syntax errors, and even if some testbench for it does not identify deviations from its specification, is not more likely to be valid when implemented in hardware, than the proverbial output of a typewriting monkey.

Validating an arbitrary design is hard. It's equivalent to the halting problem. Working backwards using specific rules that guarantee validity is much easier. Again, the point is not to produce useful designs. The generated model doesn't need to be perfect, indeed it can't be, it just needs to be able to avoid the same issues that humans are looking for.