There are several reasons why scientists choose to classify things in Latin, rather than their native language. For one, there’s the traditional aspect. Carl Linnaeus, a Swedish scientist, developed a system of classifying the world around him, and he basically started what we call ‘binomial nomenclature’ -- the two latin words, or at least words that mimic latin structure, that classify everything we’ve ever discovered. Continuing this tradition keeps the already classified things uniform within the system. Second, Latin is a dead language, which means its not likely to develop further. It’s obsolete within society, so it resists change, unlike English, or French, or any other world language. For this reason, it can be used equally by a scientist in South America as a Scientist in Asia. It’s somewhat universal in that regard. Scientists resist using common English names for plants, like you pointed out, because those words are country- and time-specific.

In regards to whether or not the classification system can be simplified, that’s a tricky issue. Scientists are continually trying to adapt and refine the classification system based on new research and discoveries. It’s not set in stone like you learned it in High School. It actually gets changed, revised, and re-edited every few years. Although it currently has six kingdoms, a few years ago it had been compressed into only three! That only lasted a brief time before it once again expanded into six slightly different categories. It’s difficult to simplify something that isn’t finished.