Why syndra's ult doesn't get cancled when she dies?

If dies after she casts her ult, it doesn't disappear. If dies as his ult is flying towards botlane, it doesn't vanish. If hits someone with his ult and dies, the person is still chained.

If starts his ult and dies, the flame still goes on to hit you.

Projectiles, once cast, do not vanish after death. Some champs have channels, some have long animations, Syndra has a short animation that is possible to cancel, just not after the balls start readying themselves to throw.