Know why?

Very often the limiting factor on the engine is a very simple thing. It's displacement. Nothing more, nothing less.

And why then does the carb opening work so lame right at almost full to full?
Because the engine designers know a couple of things that we're not considering. Like density altitude. And the range of temperatures their customers are going to encounter. And they deal with those problems by putting more venturi opening in the carb than the engine displacement is going to need at the lowest elevations or the coldest days.

And very few of us do our tuning and max horsepower comparing while checking the density altitude or what the temperature is for the day.

They place a carb on the suckers that will give guys in hot countries and high flying fields a slightly better chance of using the fixed displacement inside that engine. And most of us who've thought there was something wrong with our throttle response at WOT didn't do the observations on a really hot day at a really high altitude. (and if we did, we'd find out that the engine didn't have enough carb opening and didn't come close to full power at WOT!!)