Why in British spelling do verbs ending in a vowel plus l double the l when adding endings that begin with a vowel?

As we all know, Americans typically use dialed, canceled, councilor, cruelest, modeling, traveler, and traveling. However, British English usage is dialled, cancelled, councillor, cruellest, modelling, traveller, and travelling.

Noah Webster appears to be responsible for the sigle l spelling in AmE in words like travel, cancel, fuel etc:

• “Traveling” and “travelling” shared the same fate as many other words in the English language that have two different spellings.

• The person who’s usually credited (or blamed) for this is Noah Webster—the Webster of Merriam-Webster dictionary fame. He was a linguist and lexicographer who greatly influenced American English. Webster preferred the shorter versions of many words that had multiple spellings. He included the shorter versions in his dictionaries, and, over time, they became dominant in the United States.

• At the same time, the rest of the English-speaking world gravitated toward the longer spellings. So, while both Americans and Brits can travel, the former can enjoy traveling while the latter can enjoy travelling.

(www.grammarly.com)