Taxing unrealized capital gains is an act of desperation. What do they see coming? Stagflation, Hyperinflation, Revaluation?

Taxing unrealized capital gains is an unfathomable policy position to out yourself in and it reeks of desperation. What do they see on the horizon that they believe could justify taxing someone’s unrealized capital gains? The only thing that comes to mind is a massive and rapid increase in the value of assets due to massive inflation, planned revaluation, or collapse of the currency.