Cash also helps staff (tips) and small business owners avoid taxes (assuming they don't declare cash). Obviously depends a bit on your own morals regarding taxation.
Although tips won't be taxed, that only affects federal taxes, starts 2026 and finishes 2028 (amongst other limitations).
> or have too large denominations that people refuse
In the US, if you have actually incurred a debt (e.g. you've already eaten your meal, or you've already had the repair performed, etc), the business can "refuse" payment in cash, but by so doing, they have effectively declared the debt void.
US legal tender case law permits businesses to refuse cash for non-debt-mediated transactions, but if a debt has been incurred, they have to accept it.
> My credit cards, both the physical ones and the ones on my phone, work without an internet connection.
Of course not. I guess you haven't been to shops that say their network is down, so it's cash-only until it comes back online.
It used to be shops had those credit card imprint sliders to handle payments when phones lines were down, but nobody has those anymore (many credit cards don't even have the raised numbers anymore).
Accepting an offline transaction is at the discretion of the merchant, a payment terminal is going to be able to certify that a payment card is genuine, however as the issuer of the credit card may have the card reported stolen in its database, the merchant takes the risk of fraud in card-theft cases. So if as a merchant you have a well-known customer in front of you, you can still do the sale. Every acquirer can configure this to be more or less lenient for each issuer, and the tendency has been to be less and less lenient.
Plus I can tip easily, split bills, not have to worry about internet connections, etc