The simple answer is, because it's really, really difficult, for a very limited benefit.
Getting people to Mars is hard. Keeping people alive on Mars is hard. Getting anything to work on Mars is hard. Manned settlement (which is pretty much the only point of sending wetware there), would require underground buildings. (No magnetosphere or atmosphere really to speak of in terms of protecting soft squishy humans from radiation means you need to bury your buildings under the regolith at the very least.
Beyond that, you've also got issues of power generation once you're there, consumables and resupply (growing food at scale means lots of buildings, which means some form of underground or buried village). Plus social issues involved with sending people in a small can into space for several months, landing them and enough stuff to keep them alive (because it's easier to land rovers than humans, generally speaking).
Beyond that there's more subtle issues - comms takes a while. If anything goes wrong, it's a very long way to send help. And that's before you work on getting people back.
You'd have to plan a multi-month mission at least to just send people there and back purposefully, or multi-year mission to make it really worthwhile.
And as it turns out, every single part of it is really difficult.
Getting people to Mars is hard. Keeping people alive on Mars is hard. Getting anything to work on Mars is hard. Manned settlement (which is pretty much the only point of sending wetware there), would require underground buildings. (No magnetosphere or atmosphere really to speak of in terms of protecting soft squishy humans from radiation means you need to bury your buildings under the regolith at the very least.
Beyond that, you've also got issues of power generation once you're there, consumables and resupply (growing food at scale means lots of buildings, which means some form of underground or buried village). Plus social issues involved with sending people in a small can into space for several months, landing them and enough stuff to keep them alive (because it's easier to land rovers than humans, generally speaking).
Beyond that there's more subtle issues - comms takes a while. If anything goes wrong, it's a very long way to send help. And that's before you work on getting people back.
You'd have to plan a multi-month mission at least to just send people there and back purposefully, or multi-year mission to make it really worthwhile.
And as it turns out, every single part of it is really difficult.