Apple limits the amount of times complications can update in order to conserve your watch's battery life. In our testing, we found that complications can update around 50 times per day, before being throttled back considerably. If spaced out, this would translate to an update once every 20-30 minutes, which wouldn't be very useful.
We realized that Apple's Calendar complication does not have that same limitation, so we were able to utilize this behavior with our iCloud calendar solution. It's not perfect, since you still need to have a working internet connection and we'd we wish we could make visual changes (like increasing the font size of your reading).
That said, we closely monitor this functionality and if Apple removes the update limitation, we would love to build our own complication.