As a major perpetrator of this issue, I feel I should at least try to justify myself. As others have mentioned, the Dutch angle is often used to add drama, but in my experience, there's more to it than that. For a start, most cars tend to be pretty long and thin, if you're not shooting head-on and intend to use some level framing then you're gonna have a significant amount of dead space in both the foreground and background at the top and bottom of the frame - I'm not sure how many tracks you've been to but typically you're gonna end with some pretty manky looking fences and porta loos in the background of your shots - tilting it allows you to minimise how much those distractions draw a viewers eye away from the subject.
Another reason, that many people will like even less, is that social media has an optimal post size, using an 8:10 ratio on Instagram for example takes up more of the feed for users so gives your image a better shot at chatching somones eye - now the only way you can fit a pan shot of a race car in an 8:10 frame is to either shoot it super wide so it fits level (then you're gonna have so much space above or below it you have the previous problem) or you fill the frame and rip it at 45 degrees.
Dont get me wrong if you have control over the background, it can totally be done - but you'll find especially at places like Silverstone and Donington, the backgrounds can be pretty barren.
Saturday by
Jonny Henchman, on Flickr
ham-pan-big by
Jonny Henchman, on Flickr