Every decision to traverse a certain path will seal off other paths. It is akin to pruning. Trimming off a certain branch ensures that the pathway is closed forever. New pathways may sprout but they'll not be the same - and cannot be the same - as the previously clipped course.
Many people choose the safest path time and again. Perhaps they're faintly aware that the elected path isn't the best choice, not in the long term, but it's the path of least resistance for now.
Decisions after decisions are made. The pathways of lowest resistance are chosen each time.
Eventually, seemingly without warning, the tree of Life would be pruned into an unsightly, insipid shape. Who, then, would take responsibility for it?