In response to John's suggestion about why the ark expeditions are being thwarted, there may be another reason for the delay.
It seems likely that Noah installed some of the technology of his day in the ark. If the ark is discovered too soon, the discoverers could well inadvertently damage or even destroy some of that technology. Or on the other hand, use the technology to develop devices or weapons which God is not yet ready for us to rediscover. It's not likely that George Hagopian would have damaged much when he walked through the ark as a ten year old boy, but antediluvian technology could well be so sophisticated that even more recent explorers would fail to recognize it as valuable. Consider, for example, what we would do with a roll of wire such as was used on wire voice recorders or a DVDisc. It's been suggested, for instance, that crystals were used as a recording medium using Bragg diffraction. If so, we wouldn't recognize it even yet.
RL