Your most popular videos are content created by other people. I would start by deleting those.
You might get a few subscribers from those, but they wouldn't be interested in your new content because frankly, you didn't make inhaler man.
As YouTube continues to grow, the bar for "good" content continues to rise. With more options, consumers will always go for the easiest and most attractive products, AKA people they are already subscribed to and videos that are VERY appealing to them.
Do your videos attempt to reach that bar? Or are you defining "good content" with your own standards?