If crypto is not recognized as a spending currency, why do I have to pay in dollars taxes on staking profits?

Hello here, i was kinda wondering, if gaining crypto through staking is a taxable event, why can't I pay the amount with the crypto in question? Instead we are forced to convert to fiat and possibly trigger additional capital gain taxes on it. Just makes no sense to me.. Can't people be taxed only on fiat conversion?

Is there something I'm missing here?

Edit: the point is, why can't i just be taxed when I convert the stake rewards to fiat instead of being forced to convert instantly when I get them?