Assemblers are one of those things that's very simple for the simple cases, and then when you add more complex cases you start to think it's actually very hard until you go back and add the proper abstractions, which would have seemed needlessly complicated for the simple cases.

So people doing something trivial thinks they're easy (like this example), people trying to do a bit more think they're really hard, and people doing an entire assembler think they're easy again.