Problem with these businesses is that they can only be small. When your niche becomes considerable enough to attract VC funding to your competitors - you are to

Problem with these businesses is that they can only be small. When your niche becomes considerable enough to attract VC funding to your competitors - you are toast with that model. So probably you never get above ~$1M MRR, or even less. Which probably means an income of not over 2-3-4M per year to the founder, at best - but this is the amount you can (in Western countries) do by simply having a custom development team.