It does exist in nature all over, but it generally isn't in such a high concentration. Its like releasing 1,000 goats in your backyard. Even if your backyard could support a few goats, it will certainly be destroyed by 1,000 of them.
The end product is produced in large submersion fermentation tanks where the bacteria is first grown, then then forced to sporulate and allowed to ferment which produces the Cry/Cyt toxin crystals within the spores. Going through these phases requires precise control over nutrients, pH, agitation, and electron acceptors. Even activating the spores to create the inoculum and begin the reproductive cycle is nontrivial because of how sterile everything needs to be.
I did skim read a few papers on the subject and honestly I'm wondering how this stuff even grows naturally, everything has to be so specific it just doesn't seem possible at all.
My non-SME answer to this thread is:
1) 100 years is not that long in evolutionary terms; 2) cropland is large but not all land; 3) evolution is complex; 4) resistance is actually already observed in some species.