English is perhaps one of the most difficult languages to study in the world. Why is that? Well, it's a big convulsive mess because of many things. You may have heard of the interesting history of the development of the English Language and how it is German based with French influences. Here is a brief summary as I learned in college.
First you have the original inhabitants of England. They have their Germanic roots (I think these were the Anglos and hence how England got its name as "Land of Anglos"). Then Rome comes and establishes a brief influence in the region. After the Romans, the Germanic tribes from Europe come and conquer (possibly the Saxons? Hence you get Anglo-Saxon). It's from the Vikings that we have the "count in quantities of 12" system also known as "base-12". That's why we have words like dozen and how we have separate words for 12 numbers before your fall into the more Roman pattern of base-10. Why Roman again? Because England was then conquered by the Normans who inhabited Northern France. These people became the rulers but didn't want to contaminate their "noble language" with that of the common folk. This leads to English having a proper, French-derived word set and an Germanic-derived vulgar set. Tom Scott briefly covers this in his own video about why you swear in Anglo-Saxon. Next is even more Roman influence as you have the Renaissance. After that, you move towards Modern English where there's a global influence as English adopts words from many different languages.
However, the development history as I described is just one aspect of how the Language became so confusing. A large part of the blame stems from those who have inherited the language over generations and failed to practice proper English. Now my English skills are not great either, but I do also get frustrated by inconsistent practices that are starting to become normal. For example, the use of the for "they" for third-person singular annoys me. "10 items or less" instead of "fewer" is another annoying point as this makes it confusing how to properly use the two ("less" is for what you cannot count such as "water", but "fewer" is for something you can count, such as "items"). So when something like my latter example becomes common, it's no wonder that learning the language becomes a tedious task.
N. D. Moharo