We habitually take existence to be such a fundamental condition, in fact the fundamental condition, so that we cannot accept its negation. To say planets and stars 'did not exist' prior to human minds is taken to mean, in some vulgar sense, that they evaporate or vanish when we don't think about them, or that they suddenly sprang out of the void at the point in history when human minds were first 'switched on'.
In other words, we try to apply our daily experiential criteria to that which is before or beyond it. This is akin to the way we have trouble applying criteria of macro-level behaviours to the quantum level, or conceiving relativistic space-time distortions in relation to the standard domestic environment. But in each case the fact that it is difficult (some say impossible) to conceive these behaviours in familiar terms cannot be used as grounds for denying their validity.
