Why is the taxi credit card machine always broken?

What's up with Red Top cab drivers who always have credit card machines that are not working or they do not have the credit card slips? If this was a one time thing, I could understand but it's not. I am a regular cab passenger or I hire cabs to take our company's business associates to the airport or other destination. I am not sure why a good majority of cab driver's only want to deal in cash; maybe because they loose money paying fees, or they don't want traceable transactions....but I have a feeling there must be some regulations/guidelines governing these types of transactions. In the future, I will make note of every cab I take or get for another person, where the driver gives the same line about broken machines or no slips.