My guess is that the percentage of single founder applicants is enormous, while the percentage of single founder accepted companies is minuscule. I just wonder how big the gap is.
Given the number of people that post about looking for a cofounder here, I'm just guessing that a lot of people don't have one, but feel that they've got a good enough idea to make a business. Some of them really will have what it takes; but I'm sure the proportion of single founders that apply is quite different that the proportion of single founders that are accepted.