Was there no available data for those five blank counties?
Primaries in Texas are conducted by political parties, and they don't have primaries in every county.
I don't quite think it's totally conducted by the party, but in some of those West Texas counties, there's no county chairman.
Hansford County last had a Democratic primary in 1996.
The Democratic Presidential percentages from 1976 to 2004 in Hansford: 41%, 20%, 10%, 18%, 14%, 18%, 9%, 11%
You can see the difference in not having a Democratic Party in the 1996-2000 drop.
Ochiltree and Roberts last had Democratic primaries in 2000.
Although, I wouldn't be stunned if around two dozen or so county officials in West Texas switched from the Democratic Party to the Republican Party.