Editors are constantly bombarded with submissions. Most of them are crap, but they still have to read everything that comes in. As you could guess, this takes a long time, so expect to wait several months before you even hear a response. Fortunately, some publications list a "response time" (how long it should take for you to get an answer).

Ultimately it all boils down to a combination of the editor's personal taste, how eagerly the publication is seeking poetry at the time, and whether or not you caught the editor on a good day or a bad one. But keep trying; persistence is key.

If you've been waiting much longer than a "reasonable time" (that is, past the response time or more than 6 months) and you haven't heard a word, you may want to write a submission status query letter inquiring as to whether the poems were received. In this letter, include a SASE for their reply. If you still don't hear back, you can then 1) send a letter withdrawing your work, 2) assume you were rejected, or 3) remember to actually include your poems in the submission packet.