I think there's a PhD for someone to do a study of how and/or why some cultures don't use the final 'R'...and others accent and rrrroll the 'R's.
To me, NON-accented speech is that which comes closest to that used on TV news programs in the US. UK announcers on BBC have quite a bit of variety...and many correspondents have quite pronounced ones.

ME? I still have a bit of Mid-Western twang mixed with remnants from my years in the South..