She has always been popular, ever since her debut album, and even before. But we can't say that she doesn't know how or doesn't at all promote her stuff. Just count how many singles were put in doramas, commercials etc. All artists do it, but she got crazy with dorama promations, I think every album has at least one song that was used in some movie or drama.
I just find irritating how she doesn't put more effort in her work, when we know she can do it. Her PVs and covers got so boring, like she doesn't care at all. But no matter what, her sales are always great lol