We can kind of blame Ananda for that, as he fumbled when Buddha gave Ananada a hint. I’m saying blame in a “joking” manner, of course.
“The Realized One has developed and cultivated the four bases of psychic power, made them a vehicle and a basis, kept them up, consolidated them, and properly implemented them. If he wished, the Realized One could live on for the eon or what’s left of the eon.”
“Ānanda, the misdeed is yours alone, the mistake is yours alone. For even though the Realized One dropped such an obvious hint, such a clear sign, you didn’t beg me to remain for the eon, or what’s left of it. If you had begged me, I would have refused you twice, but consented on the third time. Therefore, Ānanda, the misdeed is yours alone, the mistake is yours alone.”
Buddha would live for that long or longer but nobody asked for that where there was time to ask.
