If OpenAI fails, and the government owns half of it...
The assets and power the government acquired for no monetary cost simply becomes zero.
The other part of simply seizing half the shares is that the government (presumably a number of ministers/officials in charge of the new sovereign wealth fund) now has half the voting power of the entire board.
That is a pretty direct way to wield influence as to the decisions the company can make, how the CEO can behave.
You want maybe the accounting to actually deprecate the GPUs they have or lease over a realistic timeframe, instead of a totally bullshit one?
Half of your shareholders now demand this.
C Suite refuse to comply?
Begin the process of firing them.