Why isn't Downtown Cab Company making any money?

When you own a property in GTAV you get cash added to your bank account each week. The Downtown Cab Company gives Franklin $2,000 dollars per week and provides him free cab fare. There isn't any reason why Downtown Cab Co would not be paying you every week. You might be receiving the money but not notice it since it notifies you through in game text message. So no screwing up cab fares don't have any affect on your payment. If that was the case I'd never get paid by the movie theaters as Micheal due to quite a few plane crashes.

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.

Sometimes you need to do quests for your business (cab co. Or restaurant etc) as owner so next time look out for such mini mission as franklin for the cab co. Then maybe you will get earnings