There is no data showing that high concentration is bad in an index.

No correlation with future returns.

On the other hand the world is leveraged to insane levels not seen since world wars or global recessions.

At the same time yields are low while inflation is high.

There is definitely a high level of risk in the financial markets.

A risk nobody, especially politicians, want to look at, because it would unavoidably lead to some major pains, so procrastinating until it's unavoidable seems the way to go.