Because of historical reasons. Americans had free texting for decades. Entire segments of phones were released dedicated to the texting experience with full keyboards. When the iphone came out it had unlimited data, but it was the exception not the norm, and it was slow as hell. People don't want to use data for something they already got for free, plus there's the whole network effect issue. Everyone has a phone number, not everyone is going to be on whatever chat platform you insisted on using. Imo I think its better this way, using this do it all technology that works on a modern phone or the flip phone my dad has, versus being reliant on whatsapp and therefore Meta.
For what it's worth all the reasons you listed also apply to the UK market, however WhatsApp dominates here so I think there's a missing piece to the puzzle.
I would guess UK has better cell coverage than the U.S. Data is too unreliable while you are out and about to be reliant on a chat app versus a text that will pretty much always reach you.
