On the occasion of Sunrise's death, I wrote about why calendar apps lag so far behind other productivity software.
If you’re a tiny startup with a brilliant idea for how to improve calendars, you face two intractable problems. The first is that the glut of free calendar apps makes it very difficult for you to charge customers more than a few dollars. Unless you can continuously acquire thousands of new customers, that’s not a sustainable business. The second is that it’s going to cost money for you to acquire customers — your best bet is probably to buy installations with ads on Facebook and the App Store. Very few companies have or are willing to spend this kind of money, and venture capitalists aren’t likely to invest in them.