The more people hate your favorite ____________, the more incentive you have to defend it. NASCAR drivers included. It's really just that simple. Kyle fans have more passionate reasons to tweet bomb that stupid contest than Danica fans, or any other fans. Kyle fans have more reasons to be on the defensive.
And for the record, I don't entirely agree with sales = popularity. In many cases, but not in all. Kyle does really well in sales. Some of it because people love Kyle, but some of it because kids love things with the little M&M's guys on it. Here's a fun exercise - stand around Kyle's merchandising trailer next time you're at a track. It won't take more than 10 minutes for you to hear a kid walk by and want something, and then a parent say "but that's Kyle Busch!" 15 minutes, tops. It's a lot of fun to watch.