You may be producing awesome video content and running a great YouTube channel, but if you don’t go an extra mile to promote it, gaining new subscribers becomes a challenge.
Think of it as a funnel. To become your subscriber, one has to find your video via YouTube search or through a referral link, they would watch it, and then if they find it interesting enough, they would subscribe to your channel.
However, it is natural for people to “fall out” at any step. Say, out of 10 people who have discovered your video, only 8 will choose to watch it, 6 will watch it till the end, and 3 of them will subscribe.
