If the government seized 75% of it, the government would be left holding 80 billion dollars worth of stock, which they can't really do anything with.
The problem with stocks is that when you sell it you have to have buyers on the other end. This is called liquidity. I doubt there are enough buyers of Amazon out there to sell 80 billion worth, so what is the government to do, just hold onto it? They could try to sell it all at once, causing the stock to crash. Or they could sell a little over time.
I suppose you could create a sovereign wealth fund with the seized assets, sort of like what other countries do with oil reserves (Norway, etc.) But all that does is create a giant, government run investment fund, which will invest in businesses, etc. Not exactly redistribution...