This is a good point. In most cities, cabs do not go to the airport unless they have to.
It just isn't a good use of their time - if you drive all the way out there with an empty cab, you've just sunk a whole lot of gas and time on a deadhead when you could have spent the same on picking up several fares downtown. And even when you have someone who wants a ride out to the airport, it's not necessarily something you want to do because then for a return fare you've got to go to the cab stand and take whoever you get wherever they want to go - which could be somewhere way out in the weeds so you still end up stuck with a dead head. That's the reason why in most cities there are actual laws on the books saying cab drivers aren't allowed to refuse to take you to the airport - without those laws, many of them would.
Maybe the specifics of my town are different, it costs ~$60 to go from my house to the airport, thats really good money for 40 minutes / 25kms. Maybe 60 minutes of spent time? (20 minutes to get to me + 40 minutes to get to airport). Expenses on a car are < 50c a km. So $12.50 in auto expenses + $47.50 for 1 hr work.
It just isn't a good use of their time - if you drive all the way out there with an empty cab, you've just sunk a whole lot of gas and time on a deadhead when you could have spent the same on picking up several fares downtown. And even when you have someone who wants a ride out to the airport, it's not necessarily something you want to do because then for a return fare you've got to go to the cab stand and take whoever you get wherever they want to go - which could be somewhere way out in the weeds so you still end up stuck with a dead head. That's the reason why in most cities there are actual laws on the books saying cab drivers aren't allowed to refuse to take you to the airport - without those laws, many of them would.