Because back then it was suburbanites who were racists and unreachable by the Democratic message, whereas now it's rurals.
To be fair, outside of West Virginia and Iowa, Bush soundly won rural America.
This isn't really true. Dukakis did well in places like Northern Alabama, East Kentucky, Western PA... In fact, I'm pretty sure that a slight majority of counties he won were rural.
Still, I'm sure that most Trump 2016 voters who were 18+ in 1988 are Bush 1988 voters.
True, especially because (1) the 1988 election had no age gradient to speak of, with most voters under 25, under 30, under 40, etc. voting for Bush, whereas in 2016 those old enough to vote in 1988 went 53% Trump; (2) many suburbanites for Bush in 1988 had moved (or retired) to exurban or rural areas by 2016.