Some blogs not ranking

Out of 120 blogs only 10-15 blog ranks.
Blogs are of different niches, eg: office chair, fan, AC etc.

My question is if I should focus on only one topic and draft the rest of the pages now. I can then write only on chairs for example.

Or is there something else to do?

Yeah, it'd be best if you stick with one niche. If you sometimes decide to broaden your horizons, make sure it's somehow relevant to the previous niche.