Oh wow, yeah that's definitely a big reason people would use what's app instead. That's wild to think about and makes no sense. Any idea why that is? Is it regulatory reasons maybe?
Nobody (other than businesses) actually pays that; people just ended up using WhatsApp for both calls and texts instead.
So in a way it's the absence of regulation: Data roaming is free within the EU, thanks to a corresponding EU regulation; before that, it wasn't unusual to pay more than EUR 10 per Megabyte (yes, Megabyte, not Gigabyte).
That's why there are prepaid SIMs without a monthly fee and unlimited incoming calls: The caller's operator pays the called operator a termination charge by the minute.
There is an incoming call charge while roaming, the rationale being that the caller doesn't know where you are and needs predictability in pricing (so the called party pays for the leg from their home country to where they are), but the EU has capped that to zero within the EEA.