Microscopes are of little use when you don't know what you're looking at---or looking for. Remember those "blueberries" they found on Mars?

And except for amoebas (and maybe Euglena) most single-celled microbes don't move (or eat) at all. They depend on the liquids they live in to bring them nutrients in solution. And biosignatures, although useful, might actually be produced by totally abiotic processes in an environment where we have little prior knowledge or experience. Remember how they found some evidence of a suspected chemical biosignature in spectra of Venus' atmosphere?

Here on earth, most bacteria are just featureless little blobs, scientists have to stain them with specialized dyes to see details in their internal structure.

As for deliberately not searching so they can guarantee future funding...well that sounds a lot like TB's explanation of how climatologists are faking global warming evidence so they can further their careers. Besides, the best fraud to secure additional funding is to fake a positive, now THAT would generate plenty of additional $.