If something this natural requires several lines of bash, something is just not right. Maybe branches should go sorted by default, either chronologically or topologically? git's LoC budget is 20x LevelDBs or 30% of PostgreSQL or 3 SQLites. It must be able to do these things out of the box, isn't it?
I used to think this but spending some time learning about xargs (hell even for loops) makes me feel like this is trivial enough to stuff somewhere.
Lots of people have mentioned awkward use cases where decisions have to be made. A built in command would have to confront those and it might not be easy
"too many lines of bash" and "lines of code" seem like very strange metrics to use to form these types of opinions.