Well, I do have danish friends which use WhatsApp a lot, but I guess you're right. Here in Spain you must have WhatsApp. Otherwise, you're literally isolated. I have free texts too but we don't use them at all. Also, it may worth mentioning they're not even encrypted and ISPs have full control on them.

So at the end of the day there're good reasons to not use SMS:

(1) 0 encryption (2) ISP's full control (3) Doesn't support videocalls (4) Doesn't support neither complex files nor previewing files (5) Doesn't support groups (6) Doesn't support voice messages (7) There're plans which don't include texts so they're not always free

The only apps I use here are WhatsApp and iMessage and I'd love to ditch WhatsApp in favour of signal but I can't.