To begin with, I'll start with a fairly popular social network - intstagram
It's not easy to become popular in instagram. To get a lot of subscriptions you need to maintain high-quality content. You need to be able to make beautiful photos, to be able to beautifully edit them. Just need to spread a variety of photos, these profiles are much more interesting to watch.
Well, if you have many pictures of the same type, then you are unlikely to have many subscribers who will follow you.