Why did God stop performing verifiable miracles?

In the olden time, He apparently walked amongst men, sent plagues stopped by a smear of sheep's blood smeared on a doorway, changed the laws of physics by creating light refraction after a flood... Why has He stopped, if He wants believers, why not create miracles a little more believable than an image on a slice of toast or a dancing sun in Portugal (when the sun didn't bother to dance elsewhere)?