Some people cannot step free of their worry even when handed information that should calm them. They are usually decent people, not bad sorts. The anxiety runs on its own and does not respond to the facts that should end it.
No job is easy for a person whose deepest urge is to do their best at what they love. The difficulty lies less in the task than in the worker's own wish to give it everything. That same trait also leaves them open to burning out again.
Even someone determined to stay mentally detached ends up tied to the people around them. Small shared moments, like eating lunch together and hearing the story behind a colleague's name, build relationships. Those ties make every job something you put yourself into, whether you planned to or not.
Someone recovering from burnout may seek work that asks for no feeling and no thought, because it seems safe: low effort, low stakes, paid and done. But any task done well tends to produce satisfaction, and satisfaction pulls you back into caring. Even when you know getting involved is risky, it is hard not to take pride in the work.
In workplaces where everyone is stretched, people are rarely openly mean. Whatever spare energy they have goes to the job itself or to their private lives. Hostility takes effort that exhausted people simply do not have.