High profile shout-outs are a sure way to success. Like Hollywood it's all who you know. If a cool guy finds you cool that cool guy will tell his followers. Those followers will then subscribe to you out of fear they would not be liked by said cool guy. Human psyche. It is also the reason why people tend to start growing quicker and quicker the more subscribers they have. Because it is easier to become part of a big group than become part of a little group.
It's all about exposure, the best thing is to just create content, have fun and leave the numbers be. Take me for example, I got 1.8K subscribers and am closing in on 250K lifetime views on my channel. This took me 2+ years. Do I care I did not blow up and have thousands and thousands of subscribers? And millions of views? Nope. That's because I do it for personal entertainment. Don't for a minute think I wouldn't love to have that though, it just isn't a requirement. And I did not join YouTube for a measure of personal worth. I did it for the love of creating content and videos I like.