Why isn't Downtown Cab Company making any money?

Solution 1:

The Wiki doesn't say that accidents such as the ones you've describe can impact whether or not the cab company can generate revenue. I'm not sure how long "ages" is as you said, but it is suppose to produce $2,000 a week (in-game time) for Franklin. There doesn't appear to be anyone else having this issue out on the internet, making it difficult to answer your question.

It has been a while since I've played the game, so I don't remember if you get a notification of some sort when you receive the money. I recommend taking note of how much cash Franklin has on him, and waiting one week (in-game) and see if his cash goes up by $2,000. This will at least prove if you actually are or aren't getting any money from the business.