That's fair. I wouldn't say that it's "we can't figure it out" but rather that "doing so takes a lot of mutations and thus resources that may be difficult to do under the table"

Sitting in a cave somewhere implies not being studied, right? Which is more the "natural mutation" thing.

Sitting in some government lab is a different story and depends on belief in scientific institutions to do science and publish peer reviewed papers and all that jazz.

Another question is how you can make a virus evolve in the direction you want. 20 years of bat evolution would not necessarily bring a furin cleavage site, so how do you make sure it does?