10-13 μm per pixel is nowhere near good enough when a typical bacterium is 0.5 - 5.0 μm in size!
I remember the discussions around the mission plan for both Opportunity and Curiosity where NASA kept making "mumbly" noises about why they can't ship decent optics with these things.
Anything that would definitely eliminate (not just "potentially find") the presence of either life or water is never included. It's always omitted, for "reasons".
Water and life must forever remain possible things for the funding to keep flowing.
Water isn't an abstract possibility on Mars. It's a reality. They've found minerals that only form in water, they've found ice, they've observed erosion. We don't understand the hydrology of Mars but it isn't some kind of conspiracy. It's a laborious process, which they continue to chug away at.
Looking for life isn't the primary mission of Mars rovers. They're remote controlled geologists. The search for life really has nothing to do with funding for Mars missions. No one expects to find it.
https://en.wikipedia.org/wiki/Thrombolite
https://en.wikipedia.org/wiki/Stromatolite
Technically, a one-foot diameter dog's vomit slime mold is a single cell.