Let S1 be the state the universe in fact had five minutes ago and let S0 be the state the universe in fact had "at" (it may be a limiting boundary condition) the Big Bang. Is S0 any more amenable to coming into existence causelessly ex nihilo than S1? Surely not! (Can one even compare compare probabilities of causeless ex nihilo poppings-into-existence?) But then why should the atheist think that it was S0 rather than S1 that came into existence causelessly ex nihilo? Neither hypothesis is intrinsically more likely than the other, and both fit our observations equally well.
The theist has no such problem, because there are good value-based reasons why S0 is more likely to be created than S1.