The US market standardized on mobile plans with unlimited texting a long, long time ago, so I think this caused people to mostly stick to SMS/MMS for communication since it was the path of least resistance. I don't know what the situation in Europe is like now, but in the past I remember it being difficult to find plans without very small SMS caps when traveling. That could be why Europeans naturally gravitated towards other messaging platforms.
Unlimited SMS plans have been a thing in western europe for the past 15 years, at least. People switched to whatsapp because you can send pictures, not only text.
MMS was (is?) spectacularly expensive, I recall sending an MMS and it costing in the realm of £1.50 -> £2.00 per message, furthermore there was a maximum size to the attachment you could send with it (100k-200k?). These two alone made it a non-starter.
Sure it was exciting at first when the first 3G colour display phones with cameras were a thing, but the cost and size limits were prohibitive when proper smartphones came on the scene.
When people in America want to send pictures without both ends having iMessage, they either use MMS (aka "text it to me") or share them some other way.
I still don't understand how SMS took off in the US. for a long time you had to pay to receive texts, which is madness.
given that undercurrent of expense, I'm still not sure why the US hasn't moved to whatsapp/signal/other. The only thing I can think of is that mobile data is even more expensive.
When you had to pay to receive SMS, WhatsApp didn't exist. Your only other options were more cumbersome things like email and AIM, which still required paying for a phone internet plan and having a capable phone.
In Argentina WhatsApp became the de-facto standard definitely because it was “free” messaging compared to the expensive SMS. The carriers ruined it for all of us.
