People using abusive language towards cab drivers

I have recently started travelling a lot from cab and i have observed people are generally rude towards cab drivers. Last time when i was travelling, the driver actually started crying after abusive words and it wasn't even his fault. I don't understand this behaviour just because they're driving cabs for their livelihood that doesn't mean they don't deserve the respect. Every other person just abuse them even if it's not the driver's fault and at the very same time if the car have private number plate then noone even tries to argue. I generally feel that people should start respecting others irrespective of the jobs they do or the cars they own. It doesn't cost anything to be kind on road or anywhere.