I'm only a former bioinformaticist (not a clinical practitioner), but people tend to anthropomorphize the blind idiot god of evolution a bit too much. "Selection" is just the end result of survivorship bias.

CGG-CGG is the most potent furin cleavage site because it works on the outer cell membranes and on the interior. Viruses that have it will outcompete all others -- but all this means is that SARS-Cov-2 with the CGG-CGG FCS has been well adapted to humans since the beginning of the pandemic and less potent mutations haven't been able to keep up. There's no "natural/unnatural" axis to consider. The most infectious virus "prefers" to be the most infectious, indeed. It's tautological. Evidence of efficacy doesn't disprove laboratory alteration.