It's like you say, Spring Boot can get you from nothing to a production ready application in no time, it is reliable and the community support and documentation is great. It is also pretty flexible, up to a certain limit.

If your product happens to be something serving a zillion requests per second, using some exotic protocol, or doing some wildly complex calculations, then Spring might not be be the best choice. And it just so happens that the HN community's primary interest goes out to these rare exceptions and not to the 99% other projects in the real world.