In France too, you might. These discussions about how strange it is to still use MMS in 2020 are starting to get old quick. Among all people, those interested in the Pinephone are probably more likely to not use WhatsApp and its friends. And there are very cheap mobile plans without much data, but on which MMS are free.
Yesterday, I wrote a script to retrieve MMS "easily" on the Pinephone (in the spirit of janky-mms [1] which does not work well on my phone and of which I'm unable to read the code properly), I need to take the time to release it at some point.
Probably in a developing country. Most of latin america uses WhatsApp, a result of carriers charging a lot of money (compared to median salary) for SMS/MMS, while WhatsApp has always been free.
When I came to the US (mid 2010's), I was surprised a large number of people never even heard of WhatsApp.
In the US they use Facebook Messenger, Google Hangouts and iMessage for sure (though not WhatsApp as you point out), but the only thing everyone is sure to have access to is SMS.
In Belgium they are quite expenseive (รง24 to send one MMS) but are more often than not bundled for free in the mobile plan.
But it never took off, I don't know of anyone using it. I must have received two in my whole life.
edit: I just checked. I can send MMS. This could have been useful. I sill send and receive SMS and I'd feel like I wouldn't try to send an MMS out of fear of the other side not getting it.