Why not everyone who I follow sends me nims
Following someone is a two-way process. You can start following people (and they will know about it), but they are not obliged to follow you in response. However, there is always an opportunity to text a person in the chat and find out why they do not want to reciprocate.
To check if someone has started following you, go to your Profile and tap on the "FOLLOWERS" section. Here you can see all the users who subscribed to you.
If you do not get the nims from your followers, it's possible that their account was blocked, or they do not have enough nims on their balance.