In Austin and other big cities in the state — Houston, Fort Worth, Dallas, San Antonio — the Texas twang is being infiltrated by what linguists call General American English, a more-or-less Midwestern accent, the standard heard on TV and other spoken media.
Blame it on the girls, say University of Texas researchers.
"The typical pattern for any language change is always the young women," says Lars Hinrichs, assistant professor of English language and linguistics at UT and director of the Texas English Project. "If you pronounce things the new way, you have power — you're hotter. The more popular girls lead the way." ...
... "Who's picking up on this new transition? It's not the old people. It's the young people doing it," Hinrichs said. Young white females are the earliest adopters.
And like other adaptations that are steadily transforming the Texas accent, it emerged first in Dallas and its suburbs. Then it spread to Houston, then on to Austin and San Antonio, he said.
Emphasis added. I'd bet that the diffusion of General American English followed the same road those from out of state used to move to Texas. The local agents of linguistic change have to compete with the new girl, whom all the boys are chasing. We seem to be hardwired to mate with migrants.
A major variable to geographic mobility is gender. Women are more rooted in place, figuratively and literally. To be crass, a woman on the move is a whore. She's attractive because she is exotic, which makes stuck locals very uneasy. The traditional power hierarchy is upset. Migration is too damn sexy.