Bitcoin or any other cryptocurrency is not accessible to all payers or payees. It depends upon the audience, Perhaps a niche cryptocurrency or decentralization project could receive donations through cryptocurrencies primarily as its audience likely have access to it.

Besides, legality of cryptocurrencies is highly volatile around the world, I already pay taxes for my donations via Stripe for my projects as Stripe doesn't support non-profits in India!

But I agree with you that one of the main premise of cryptocurrency is to do away with middlemen and thereby commissions; Then again there are commissions to exchanges but may not be for every transaction as when paid through card via Buy Me a Coffee/Stripe or similar services.