Maintain equipment, build new equipment, take data, design and re-design experiments, run experiments, and fix any of a thousand unexpected problems, any one of which would kill a robotic probe dead in its tracks.
Add to that the "little tiny" problem with using robotic probes---TIME LAG--imposed by that un-impressive phsical law called "the speed of light". Robotic probes now (and for the foreseeable future) are not sufficiently autonomous to work completely without human intervention--and the further away from earth they are, the worse the problem gets.
As to "sending and ARMADA of probes"---a combined manned/robotic approach would actually be cheaper--to wit--with a permanent manned presence in LEO, you actually build the probes in and launch them from space.
And no, Virginia, I don't suffer from "a lack of inspiration". I think that's YOUR problem.
The program is dead in its tracks, right now, because a group of human "probes" were killed.
The nice thing about robot probes is that they only cost money. Nobody's heart breaks if they fail and collapse. For what we spend providing rides, we could develop lots and lots of probes, most of which would fail. Then we'd need more and more probes. Every one would be better than the last. Probes don't need to breathe, and they don't have to come home.
And astronauts are not exactly perfect. I seem to recall a camera burnt to a crisp moments upon making a moon landing.
Think of the spinoffs, the technology that would be developed.
And, we'd actually get to see and hear Mars, for ourselves, not vicariously.