Non-scalable things usually can still scale to tens or hundreds of customers, and those first tens or hundreds are the hardest customers to acquire for startups. The hardest thing for startups is to get started (hence gain insights to what problems are most important to solve first), and these non-scalable things are the fastest/easiest ways to start. For typical hackernews readers, solving problems and scaling are usually not too hard (challenging but quite doable), but getting started fast and finding THE problems are very very hard and often not fun to do.