I think you just haven't discovered you can? I don't know of anyone arbitrarily looking through logs, but it's incredibly useful with git blame when you get to a section of code and don't understand it or typically it's done in an odd or unintuitive way. The blame shows who wrote it, information as to what they were working on via the actual commit message, and branch information.

If the person still works with you, you can just ask them about it.

If they don't or you don't want to bother them, the commit message tells you what the change was and often times why to give you a better context.

All the teams I've worked on included information like feature, bug, defect, and the associated ticket number in the branch name, so you have the information at hand to go look at the ticket directly and see what requirements were needed.