Logically, a lot of pirates - and seafarers in general, come from coastal towns, and the southern coastal towns of Britain will have supplied an above average number of sailors and pirate types.
The main reason is Robert Neewton, who hammed up his performance as Long John Silver in the best-known version of the film 'Treasure Island', and his vocal embellishments have adorned the cliched pirate character in films and literature ever since.
Most of the English speech was rhotic right up intil the early 20th Century. Rhoticity is notable from the use of the rolled 'r' and is found primarily in Hiberno-English, Scottish English, and West Country English.
Most of North American speech is also rhotic, English was in most places in the 17th century. By the late 1th Century elocution lessons became fashionable and the advent of renounced pronunciation came along.