Because, ‘merica.
This sort of nonsense doens’t happen in Australia because we’ve been using contactless (PayPass & PayWave) for almost a decade, and Apple Pay is simply a (better) version of this, which works on all the same terminals - from big stores to farmers’ markets. I haven’t used cash here for over two years since I’ve had the Apple Watch with Apple Pay.
The situation in the USA is a bit of a mess. Last time I was there I used Apple Pay where I could, but many places required me to *sign* for a purchase - my card didn’t even have a signature on it (shows how often I use it), so I had to sign it first!