sadly you may have a lot of inactive subs, or people who just aren't interested in your content despite subbing to you (they may have just liked one video of yours assumed they are alll the same and subbed to you), some people only sub to you in the hope you will sub back, they may even comment something nice to make you look at their channel, then you have the ones who tell you they have subbed and it's obvious they haven't. I have the exact same problem i am not getting half the amount of views that I should, it's slowly improving but you just need to keep working at it, i know the pain it's great seeing so many subs next to your sub count but then people look at your views and it's like oh...
Try changing up your thumbnails you need more bright colours and maybe little cliparts or something to catch peoples eyes, and just keep uploading videos as one day you may make one that goes popular really quickly, i have uploaded a 3rd one recently that's doing pretty well and i never expected it too and gained at least 30 subs from it so don't give up