The point is that the Buddha did deliberate shorten his lifespan for which Ananda tried to beg him not to do.
For all intents and purposes, going off "life-support" knowing full well the resultant death that will occur from it, is suicide.
Buddha has done his mission, and he didn't owe anything to anybody.
"Life is a struggle. Life will throw curveballs at you, it will humble you, it will attempt to break you down. And just when you think things are starting to look up, life will smack you back down with ruthless indifference..."