It's a loophole the mega-rich are using to avoid tax.
The other thing that's happened is that a lot of the mega-rich have lobbied to gradually chip away at inheritance taxes. So again they just pass the asset, paying a fraction of the taxes they'd have paid had they been a "normal" tax payer.
And one of the big things they've got? No capital gains on those stocks when passed to children.
So yeah, we need to tax assets as well as income. Because anything that's not taxed the rich just funnel money into it to avoid paying tax.