Individual codebases can already include stack traces as they see fit, so studying only a single codebase would be rather pointless. If an individual codebase benefits from stack traces, it will use them! The study looked at how often they were used to determine if it would be a useful default. It found, by looking at many different projects that had stack traces included by default, that it would not be useful to include by default. Especially in light of the cost of inclusion. Adding stack traces is definitely not free.