Firstly, when lower PR directories increase in PR, they tend to charge for submissions, i.e., become paid directories and by not submitting to these directories now, you could lose out on getting a free link from a quality directory.

Secondly, by choosing to submit only by higher page ranks, one could possibly lose out on links from directories that have the potential to increase from PR0 to a higher PR.

For these reasons, submitting according to PR is not always recommended.