I can buy this potential explanation. I think it's a combination of factors. Enforcement of payment network rules is likely a contributing factor.

Beyond that, the predominance of USD denominated cards in the US makes it less lucrative for a small business to enable DCC on a standalone terminal. For instance, at a souvenir shop in NYC, what percentage of transactions will still be from USD cards versus a souvenir shop at a major cruise port city in Europe seeing cards denominated in local currency, especially for places not using the euro? You also mentioned not seeing DCC on Toast, Square, and equivalent terminals, which are ubiquitous in the US at small and independent merchants.

Finally, customer service attitudes, the indifference of many retail employees, customer facing terminals in retail settings, and self checkout options all favor the customer's ability to avoid DCC. When my sister-in-law saw DCC in a couple of retail environments with her AUD card, it appeared that the cashier didn't have any control over the currency selection. I say this because I asked her to wait for me to take a photo, and the cashier seemed to be waiting for input on the customer's part. One of the few cases where the customer wouldn't have access to the terminal would be in a restaurant, but customer service (and the prospect of a bad tip) would avoid DCC there. It's not like elsewhere in the world where from our own experiences staff seem to be trained to direct or force DCC upon customers. We've seen multiple posts here of people asking employees to opt out of DCC proactively, and the employees feigning surprise by replying, "Let's see what happens. Oh, it looks like it charged in your home currency. I can't do anything to fix it."