Simple answer is for the same reason that they don't maintain an official changelog. There's a lot that gets changed. Tiny things, small scale things, then big scale things. The perspective of whether it's big or small depends on the person looking at it.
For example, the CSS change? I shrugged it off because it was pretty minor to me. But given the reaction, there's a lot of people in both camps - some found it minor, some found it major. Both camps reacted differently - some felt it was minor but could use some big changes, others felt it was a major change but also shrugged it off. It's not even like there's a universal opposition or appreciation in either camp.
Could the decision to pre-advert or not be considered arbitrary? Perhaps it can be. Fact is, not everything goes through the community because making everything go through the community would probably hold up development significantly. By asking only about the biggest of items and letting much smaller things just get pushed, it accomplishes a lot more in less time.