I think that there are plenty of optimistic country songs. However since country is a direct descendant of the blues, it's not exactly a mystery why a good portion of the tunes are a bit melancholy. If Clarence "Gatemouth" Brown sang only happy tunes, his record sales would be in the toilet. It's our nature to want to know that others are dealing with some of the hardships we endure. Even if they live in a five million dollar home in reality.
The genre is way too diverse to generalize, especially in the last 20 years. If you really scrutinize all genres of music, you'll find that country music is not disproportionate in terms of racism, current events or even trailer park antics. It's the genre that people love to kick around, even while record sales are at an all time high. Garth Brooks is surpassed only by Elvis in record sales for solo artists. That speaks for itself.