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.

I remember MMS being both expensive but also often broken as each user had to set up a bunch of APN in his phone. And the image quality was crap.

I'm amazed it's still a thing in some port of the world.