The reason is this: I took stock of my inventory this past weekend and discovered I have already accepted more than enough poems to fill Mythic Delirium 23, which will be out, assuming all circumstances cooperate with me, in October. This is a testament to the quality of submissions I've received since reopening this past November.
My goal is go ahead and fill Mythic Delirium 24, with a target publication date of March 2011. And with that task done, staying open longer would just mean ridiculously long waits between acceptance and publication, so I will shut the spigot off until it's time to put together Issue 25.
It's not likely to affect many readers here, but when I reopen again, I intend to shift to online submissions only. Sad to say, what postal submissions I receive now are so few and far between that if I don't respond to them right away I tend to lose track of them. (Subscription checks sent through the mail will remain welcome, of course.)
So: now reading for Issue 24 until May 23. Take your best shot.