Les thinks that website advertising is coming to an end. Google is taking more of the pie and ad revenue isn't really there anymore because AdSense has changed. He isn't really sure how that is changing, but he needs alternatives to raise more revenue from his website. Leo says one of the reasons that ad revenue is dropping is because usage of AdBlockers is exploding. People don't want ads on their surfing experience because they believe they're being tracked and they don't like the fact that it slows down loading times. It also goes against mobile bandwidth caps. But that's how a lot of websites pay the bills. It's not that Google is taking a bigger cut, it's that there's less ad revenue because people just aren't seeing the ads. So sites are being forced to fold.
Leo also wonders if skipping or blocking ads is ethical. If you're not looking at ads, how can that free content remain free? What you'll end up seeing is more ads in content with product placement.