I can see the issue as a circular trust one given precedent's magnified power in government that it multimillion dollar salaries would wind up proliferating and abused for ones who don't remotely have talent and any metric to try to limit it would get specification gamed to hell and back.

It seems to be a Morton's fork of expertise and stakeholding separation. If they are of the bueracracy they may be tempted to use it to exfiltrate wealth to cronies. If done by a ballot initiative they by definition wouldn't be informed at large about specialist topics (if they were it would fail to be specialist) and would be outside the context.

Being willing to pay a million for proper results would be a good deal but the devil is in the details for how to do it right systemically which is hard even before dealing with people in the system.

It also reduces corruption. One of the things Singapore did was to pay top salaries to government employees.

Like others have pointed out, many times people see the government job as a stepping stone to a cushy private job where they will make the real money. Thus, government employees treat the big companies with kid gloves because they don’t want to jeopardize future employment. If instead, the government job actually paid a competitive salary, they would be more focused on their current position and not trying to make sure they kept their future private employers happy.