If you use YouTube much, or if you're someone that makes videos, then you're already familiar with one of the fundamental ways YouTube is broken: it doesn't always show people the latest uploads, even if they're subscribed to someone.
It's a system that's crappy for both viewers and content creators. Fans don't get to be up-to-date with their favourite videos, even though they have basically told YouTube that they want to see it all. And creators can't grow their channel, which is particularly worrying if they're relying on YouTube for an income.
The Game Theorists go into why this happens. Basically, they theorise that the way YouTube works is that, the more a person engages with someone's content, the more likely YouTube is to show them more of that channel's content. It's a system that sounds like it should work, except it can still screw people over.
An example: Pewdiepie's channel is ginormous, and he uploads stuff nearly every day, but because of that output, people can't keep up. And because they can't keep up, the system is more likely to not show them the latest uploads -- they're not engaging, after all. Which means they're even less likely to be able to keep up.
It's not a problem unique to Pewdiepie of course, it's just easier to see just how big this problem is with a channel of his size. Everyone has to suffer the fact that only a small percentage of their overall audience ever gets to see their videos thanks to the system, even though they have told YouTube they want to see all of it.
That said, part of the problem here is figuring out the sweet-spot, in terms of frequency of uploads. You also have to consider what you upload, since the content and angle has an effect on your views, too. Really -- everything Game Theorists talk about in this video is fascinating, as it gives an inside look at how YouTube's systems work. If you have the time, it's worth the 14 minutes:
Game Theory: Yes, PewDiePie. YouTube IS Broken [The Game Theorists]