While going through the vast stretches of English grammar, I have often felt that some of the rules governing it are a bit perverse and illogical.For instance, why don't English people say crafts, aircrafts, sheeps and deers?
And why do hunters and poachers use the same form for some game birds and animals? Are there any logical explanations for these apparent anomalies?
I am sorry - you cannot expect a language that has evolved over 1000 years to be logical. There are far too many influences and origins.
You need to start looking at etymology in order to understand the anomalies. This is a useful site: Online Etymology Dictionary
Learn to live with the unexpected - it's far less wearing on the nerves!