Maybe it needs to become as popular as Tokyo Ghoul or Kingdom in order to get an anime.
Lol that'll never happen. It's like saying Toriko reaching the same amount of sales Bleach had during the Arrancar and Aizen arc. I don't know for Nejimaki but the other series have already reached their highest point. Only a really good anime adaptation could make sales increase.
If you say that, then why there isn't anime for Usogui?
Couldn't say. I don't read Usogui. I never said 'Oh why is this really popular manga not an anime', I simply asked rhetorically why it is not animated. Besides that, while popularity is a help on the road of gaining an anime adaptation it isn't the end all be all.
That being said, I'd be fine with a Nejimaki VOMIC at this rate. It just seems to be a shame that it doesn't get anything despite lasting for three years almost.
Saike Once Again (Hiatus)
Nejimaki Kagyuu (Ended)
Hitoribocchi no shinrakusha (Monthly)
Majimoji Rurumo (Monthly)
Tenshi-chan & Akuma-kun (Ended)