I think it all depends on your industry or environment. Yes there are a lot of people that don't feel the need to keep one around, or tried it for a while, but have decided against it. I don't know if its because the average belt has become heavier with the rise of the smartphone, or its just a general attitude towards "knives" in general. But in some places they are still very much a part of the uniform, theater and stage techs, film crews, and the like still rely heavily on multis, despite a few companies trying to make dedicated tools.
I would say that in general, they are just as popular as they ever were, its just that more people go for the heavier models and keep them in a bag rather than on a belt.