To pay with my credit card online I just need to fill in the card details (which are often stored on the website anyway, or auto-filled by my browser). To pay with card in person, I just need to touch in my phone (at worst take out my card and enter the PIN if they don't accept contactless, which is exceptionally rare in the UK).
To pay with a cryptocurrency I need to:
1. Be using a service which accepts crypto. This immediately rules out the overwhelming majority of services people use, live or online.
2. Own the same cryptocurrency which the service accepts.
3. To have it, I need to register to a cryptocurrency exchange.
4. To do that I need to go through identity checks and often message support a couple of times for one thing or another.
5. Now I can use a payment method to deposit money from my bank account to the exchange. NOTE: This step alone is slower than the entire process of just paying real money with my credit card.
6. I need to wait a couple of days for the bank transfer to the exchange to clear. The transfer also comes with fees.
7. While I'm doing this the price of the cryptocurrency is fluctuating and I have no way to know which way it will go next and by how much.
8. Now I need to transfer the cryptocurrency from the exchange to my wallet - this process is different for each coin and each exchange.
9. A few minutes later, if I've followed the instructions correctly I may have the privilege to pay with a cryptocurrency from my wallet. I will pay a fee for this and the payment won't be received immediately.
And I'm capable of doing all of this because I'm a somewhat technical person who's used to following instructions written by other people and has a basic understanding of cryptocurrency. Neither the older members of my family, nor the younger ones who don't spend their entire day in front a computer will have the ability or interest to go through this.