Mixing things up keeps the trip interesting instead of doing one activity the entire time. You'll get bored fast if there's no variety in what you're seeing and doing. Cars just don't cut it in that city because you're sitting there burning daylight while everyone else is doing the same thing. You can check out motorbike rental in Jakarta here https://getrentacar.com/en-US/motorcycle-rental/indonesia-jakarta . You zip around the city on your own and actually cover ground. See what you came for without half your day disappearing just trying to get somewhere.
