Information technology - and contact, in general - is at most the "grease" smoothing out this sort of change, not the cause itself. The actual cause is usually social and ideological. Nationalism, lower prestige associated with the dialect in question, this kind of thing.

That happens because we use speech itself to highlight who we identify ourselves with.

Another thing to consider is that a lot of traits usually associated with Southern American English ended associated with African American Vernacular English instead - non-rhoticity, gerund in /n/ instead of /ŋ/, etc. So at least in this case this might have a component of racism (I do not know if it does), where locals would rather be associated with whites from another region than with black people in their own region.

For contrast: in Brazil I've been informally noticing the opposite trend, at least in my region, with kids sometimes having a thicker accent than even me (and my own is already thick), with the accent levelling being mostly local between the rural zone and nearby urban centres. Info tech is still everywhere here, and those same bloody kids don't stop staring those bloody phones because of their bloody ~~zapzap~~ WhatsApp, but they still prefer to speak like locals instead of adopting somewhere else's accent. (I'm mentioning kids because dialect change is usually cross-gen.)