It is one thing to make a nest (birds etc do that) and quite another to make a functional fish trap. The lack of evidence of stone tools use by BF is just that and considering how little contact we have with BF, I do not consider it evidence of anything other than we know little about the daily activities of BF and have very little contact with them. Clark and Skamania county were at one time heavily settled by First Peoples who used stone tools and other cultural artifacts but in spite of nearly two decades of field work, I have yet to find so much as a single arrowhead in the field. That makes it even less likely that someone would find artifacts left by BF, and if they did, how would they know the difference between that and first peoples artifacts? The rock pits near the top of Silver Star Mountain have been assigned to NA activity but local tribes have no knowledge about their use in their oral histories. Similar rock pits in the Oregon Cascades seem to have links with BF activity harvesting small animals.
My guess is that at some point some gene turned on parts of the human brain that envisions constructs and making things. Causing humans to diverge from BF if they had common ancestors. Humans in some parts of the world took up agriculture fairly early and leaped ahead of hunter gatherers in developing technology and fixed settlements. Agriculture enabled a more consistent food supply, reduced the time dedicated to food gathering, and allowed humans spare time to experiment and create. Even today the most primitive humans are those that are nearly full time hunter gatherers. Perhaps BF is stuck in the hunter gatherer role and cannot break out of it. I have to think that competition with humans have just made life more difficult and primitive for BF. Perhaps even to the extent that they used to use fire but had to give it up because it attracted human attention.