Here's why:
* Sound and Pronunciation: In English, we don't usually double consonants if they are already pronounced clearly and distinctly. For example, "bat" and "bet" are easily differentiated, so doubling the "t" in "bat" wouldn't add any clarity.
* Word Origin: Many English words have roots in other languages (Latin, Greek, French, etc.), and these languages have their own rules for consonant doubling. Sometimes, doubling a consonant in English is simply because the original word did.
* Spelling Conventions: There are some spelling rules in English that dictate when consonants are doubled, but these are primarily related to vowel sounds before the consonant.
Examples of Consonants Rarely Doubled:
* L: We rarely see "ll" at the end of a word (except for some exceptions like "skill").
* R: Doubling "r" is uncommon, but it can happen in some words like "mirror."
* X: "X" is rarely doubled because it is already a combination of "k" and "s".
Remember: English spelling has many irregularities, and there are always exceptions to the rules.
Instead of saying "seven consonants cannot be doubled," it's more accurate to say that some consonants are rarely doubled in English due to pronunciation, word origin, and spelling conventions.