Re: Why these techniques?
There are many forms of jiu jitsu some have different emphasis since it has different origins.
The technical syllabus that aikido came from was on a type of jiu jitsu that was part of a weapon based martial art system. Thus the different emphasis.
Jiu Jitsu as you know today is more of a blend of different jiu jitsu methods rather being part of complete martial arts system based on the used of weapons.