system
Given the following post, respond as if you're commenting on Reddit:
human
Why isn't Ceres considered the main target for a manned space mission?

If we ignore for a moment the counterproductiveness of interplanetary human spaceflight why isn't Ceres deemed the prime candidate for such a mission?  It clearly has some important advantages over the most frequently mentioned candidate, Mars:  

* Ceres has much more frequent launch windows to/from Earth than Mars, one per 467 days in comparison to one per 780 for Mars
*  it has a much smaller gravitational well, the gravitational acceleration on the surface of Ceres is only about 2.8% that of Earth
* its upper layers are very rich in water, it is thought that there is more water on Ceres than there is freshwater on Earth.
gpt
3 Main reasons

According to Wikipedia: 
> The unmanned Dawn spacecraft, launched by NASA in 2007, is en route to Ceres. The probe has been orbiting asteroid 4 Vesta since July 15, 2011. After completing one year of explorations there it will continue on to Ceres, arriving in 2015, five months prior to the arrival of New Horizons at Pluto.[28] Dawn will thus be the first mission to study a dwarf planet at close range.

* We haven't had a chance to study it. NASA is very unlikely to send a manned mission to a celestial body that it hasn't had the opportunity to thoroughly study beforehand

* The Asteroid Belt is dangerous. Sending a probe to Celes is of no consequence, but it is very unlikely that NASA would be willing to risk the safety of its astronauts (and its budget) on such a mission with current technology. 

* Distance. Celes hangs out at around 2.766 AU. Mars is at 1.523 AU. Current technology wouldn't be able to get astronauts there in a way that is practically and economically feasible.