You just have an interest in different parts of the stack. Someone could write the same thing, but instead talk about why they needed to understand how the computer hardware was implemented to run the programs and even needed to build a small computer themselves to get a feeling for what the computer was "actually doing".

Alternately, at a systems design level, the constraint may not actually be the implementation of the components, but the organization and production of the system. This could be a simple CRUD app, where the business domain is more important, or the manufacturing of a new toy, where cost retooling and speed of production matters significantly more than trying to make the toy of a slightly higher quality.

There is a LOT of complexity out there in the world, and most people (on hacker news especially) gravitate towards parts of that complexity that interests them. A lot of other people gravitate towards different problems, which is a good thing, because it takes all sorts of specialties to get something nifty off the ground.