Holdover of them being obsessed with SMS for some reason too.
I remember having to pay 20c per SMS and 50c per MMS before IMs on phones became a thing. Wasn't hard for literally everyone to want to change to the first available client which for most people was WhatsApp, 2 years before iMessage was even released. Guess messaging was so cheap in the US that they didn't have a good enough reason to hop on the IM train for years.