People that want to evade taxes should use cash Also, no one is paying for coffee with on chain bitcoin txns (strawman fud). People will most likely use ecash which has plenty of privacy
You’re correct cash is popular. However, cash has local theft risk and can’t be used online. Ecash is custodial is it not? That’s the opposite of privacy, a third party can see all. Coffees could be private with bitcoin lightning layer 2, but how many people are going to fork over $500+ to setup a self-custody node? That's my point
I used to buy coffee with on-chain transactions all the time up until 2017 when I left cryptocurrency entirely for five years because of the transaction fees.