Suicides always have victims beyond just the deceased. In most cases, the casualties are merely grief-stricken, so we really don’t think much about them. In this case, the person who committed suicide just happened to take a few people with him, that’s all.
The difference between this suicide and that of the 9/11 hijackers is intent; they intended to kill as many people as possible even if it meant dying in the process whereas here we have a pilot that wanted to to kill themselves even if it meant killing a few other people at the same time.
If it is later discovered that there was ANY motive other than just offing himself, I am sure investigators will turn something up. Until then, I suggest we leave it to investigators.