Because if it didn't, we would NOT exist. We could never have been born, never think, never have blood flow, etc.
Just nothing. No sun, no planets, an empty vacuum, but enough tremendous ENERGY that matter resulted, he start of the 'big bang'.
With matter came gravity, and with gravity came time. Lots passed, and eventually conditions on our lump of matter spawned life.
Lots more passed, and eventually WE evolved. WE then had TIME at our disposal. Without it, YOU could never have existed, let alone asked the question!