I can do this in like 5 seconds with my PiHole and not only am I not a network engineer,
Exactly and consider Cloudflare for instance, adding an “if domain block” is easy but then once you’ve thousands of servers running the same piece of software across the globe deploying updates and features becomes way slower and way harder. You’ve to consider tests, regressions, a way to properly store and sincronize the blocklists across nodes etc…
I'm not saying it can be done, because it can. But it will take longer and it will be a problem for someone. Besides you only have that point and click interface in your PiHole that allows you to do it in .02 because someone spend a few hours developing the feature. :)