I.e.: they don’t carry high power microscopes because apparently there’s no room for one on a 900kg rover the size of a car.
They do though:
"The WATSON (Wide Angle Topographic Sensor for Operations and eNgineering) is a reflight of the MAHLI (MArs Hand Lens Imager) that is a part of the Curiosity rover (Edgett et al., 2012). WATSON obtains full-color images from microscopic scales (∼13 μm/pixel) to infinity and is used for initial textural analysis of rock and regolith targets, as well as to assess potential proximity science targets and the safety of robotic arm activities (Edgett et al., 2012). The ACI (Autofocus Contextual Imager) is a fixed field, 10.1 μm/pixel resolution grayscale imager used to obtain best-focus and colocate laser spots with surface feature analyzed during SHERLOC spectroscopic investigations (Bhartia et al., 2021)."
From: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022EA00...
See also:
https://en.wikipedia.org/wiki/Perseverance_(rover)#Instrumen...
https://science.nasa.gov/mission/mars-2020-perseverance/scie...
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.