After George Wallace lost his first race for governor of AL in 1958 to a candidate who went to his right on racial issues, it is said he vowed "never to be 'out-segged' again."
In 1978 Bush lost a close race for congress in West TX (the Lubbock-Midland area). In that campaign, his opponent criticized Bush as a carpetbagger, and ran TV ads featuring someone in a car with Connecticut license plates repeatedly stopping to ask directions.
My theory is that, similar to Wallace, Bush made a vow "never to be 'out-Texaned' again," and adopted his phony accent.