To add to your point, the phrasing of "$1K in a decade" seems convoluted to intentionally try to over-emphasize the cost. A much more fair/normal way of phrasing that cost would be $100/year, or $9/month, which is very little for someone who has the time and energy to write their own and gets enough value out of it that they find that worthwhile.

The tradeoff doesn't make sense otherwise. If you're poor, then you wouldn't have the luxury of the available time to write your own PKM - the opportunity cost is huge, it's massively preferential to use an existing free solution that is "good enough" (Obsidian without sync or using your own sync solution, Dendron, Roam, Org). If you're not poor, then $9/month is a rounding error, especially compared to the value provided.