I think there is a huge gap between "substantial revenue" and unicorn. I have no doubt that these platform can be great businesses, bringing in tens of millions of revenue or profit per year. But when you take on $100M in investor money you are forced to either go big or go home. And going BIG seems really hard with a newsletter or Medium-like business that has little defensibility. Of course, for the founders this may still end up being a great deal and the right choice, even if the company eventually fails.