I’ve never understood why they don’t have a powerfull microscope on board to look for life and prove it beyond doubt.
There’s a good chance you wouldn’t know what you were looking at in a visual-spectrum microscope if an alien microbe happened to turn up under your lens (there actually are microscopes). Consider the advances in scientific instrumentation which have occurred since the 1700s when the compound microscope was invented, especially those measuring chemical reactions. Chemical signatures can be much less ambiguous when they measure inputs and outputs from a biological process, even if you don’t know exactly what to look for when you design the sensors.