The first 2 poetry magazines I was published in - one was a small student-run local production, which I consider to "hardly count." However, technically, it was the first. The second, which was the first one I was not affiliated with in any way, to publish my work - well, while I sincerely appreciate their publishing me, and I was thrilled at the time, and continue to be thrilled that someone "opened a door for me," I was both pretty sure they would accept my work and fairly certain I was better than at least some of what I saw published by that magazine .
So there was not so much "why me? why now?" as "Yes! My expectations were validated!" combined with a tiny bit of hollow triumph as I did not hold that poetry magazine in stellar, sterling high regard. Like "I could have done better/tried harder/submitted to more challenging markets." 
In other words it's almost the opposite of what you imagine, for me personally.
Much more often, though, I am left wondering, "Why this poem?" Poems I've written that don't impress me that much often get accepted. Once or twice I've reread them after acceptance and thought, "Really?" This is why it does not do, too much, to worry about whether you like your poems when you submit them. It's really all in the eyes of editors, and I have no insight to them.
The one poem I've had accepted at the most prestigious publication I've been accepted in, so far (and that has since sat on my poem and put it in publication hell for like, 6 months and 1-2 issues now), I did very much enjoy, but I thought was generally a bit weird to be published. I was really shocked, but extremely pleased, when it was picked up by a journal with such a big name and following as the one it was picked up by. It still feels false, like somehow I tricked the editors - like they didn't really know what they were accepting.
Every poem I submit gets submitted round-the-house to multiple poetry magazines, so every poem, in much the same format and words, is generally rejected by a shit-ton of places and accepted by one, if any. So I don't think I can say I can convince myself my rejections are different. It really, really comes down to: - did I get the editor on a good or bad day? - does their taste align with what I'm writing? - do they like what I have to say? - did I execute the poem well? etc.
One of the poems I just had accepted I've shopped around at 10 places before one took it. I had a lot of belief in that poem which is why I supported it so much. Usually after 3-7ish rejections I'll retire a piece and come back to it after a few weeks or months and see if it's still as good as I think and if I can improve upon it. Then I decide whether to send it back out or not.
 Note: "pretty sure they would accept my work" is a faulty metric. There have been many magazines I was "pretty sure would accept my work" that have absolutely not, whether with personal rejections about how I should try again and they like my style, or not.
It's an insane process. What goes up online is probably less than 1% of everything I write.
 Also can be a faulty metric. See magazines publish what I consider "crap poetry" but that still won't publish me. Taste, natch?
 This voice comes in almost every time I am accepted somewhere. It is not worth listening to. If I listened to it I would never be published, ever.