A bunch of sellswords went to town to stab my gut out and the guards just stood there watching. While fending off the ruffians and getting close to the guards, one just proceeded to step away from us and said "My money on the big one". This is where my taxes are going? I saved you godforsaken town many times from dragons and this is how you repay me? Why don't they help me?

Guess the guards don't mind if sellswords kill other sellswords?

Hey watch your mouth, milk drinker. I joined the mage college and i'm not a filthy barbarian that murder people for a few pennies. The mages HELPED me,(cough, sure some of them ran away, but it was better than just standing there watching me being stabbed in the [censored] kidney for fun.). The guards can [censored] themselves next time a dragon appears and there will be a next time. They can turn to soil fertilizer for all that i care. And i swear i'm gonna thrall the ass of that guard that made that snickered comment.

Nords don't like mages, there you go

radiant ambivalent... uh AI?

Based on the dialogue, I'd say the guard AI got triggered in brawl spectator mode

I was disappointed to find no guards helping when a dragon turned up outside Whiterun, even though they spend half their day whining about not getting to kill dragons like their cousin does. They can be delightfully useless.

Yeah i was guessing to be a bug. Or not like someone here said. Maybe it is just a tid bit of the radiant AI. I'm a breton too if that counts to the racism.