To be fair, most senior developers don't have any incentive to put this amount of analysis into a working codebase. When the system is working, nobody really wants to spend time they could be working on something interesting trying to find bugs in old code. Plus there's the social consideration that your colleagues might not like you a lot if you spend all your time picking their (working) code apart while not doing any of your tasks. Usually this kind of analysis would come from someone specifically brought in to find issues, like an auditor or a pen-tester.
The right incentives would motivate bug hunting, it entirely depends on company management. Most competent senior devs I’ve worked with spend a great deal of time carefully reading through PRs that involve critical changes. In either case, the question is not whether humans tend to act a certain way, but whether they are capable of skillfully performing a task.
Unfortunately some senior devs like myself do care. Too bad no one else does. Code reviews become quick after a while, you brain adapts to being to review code deeply and quickly
