Why? Apparently, it's because Walker wanted to be seen with Obama and Mary Burke did not want to be seen with Obama. So, again: why?
Citizen Dave (former Madison Mayor Dave Cieslewicz) says that Burke didn't want to seem "too close (metaphorically and literally) to an unpopular president," and Walker chose to highlight "Burke's unwillingness to stand with the president symbolically." Walker "had nothing to risk."
I'd put that more positively: Walker is a Republican hanging onto his popularity in a blue-to-purple state, and showing his relaxed camaraderie with Obama makes him seem moderate and able to work with others. It's similar to Chris Christie, when he was up for reelection in 2012, walking with Obama amid the wreckage of Hurricane Sandy. Except Christie was making a play for help after the disaster and risked looking as though he wasn't conservative enough for Republicans who might reconsider whether he's the right fit as a 2016 presidential candidate. But Walker needs nothing from Obama, and he benefits from looking capable of relating to Democrats. He's in no danger of seeming as if he's secretly liberal. His conservative credentials are firmly established, and no one would think he was aligned with Obama. So he's free to do photo ops just to look friendly and normal... and dignified and substantial.
But back to Burke. The President, her party's leader, comes to her state, and she avoids him? Citizen Dave says that "Burke campaign's strategists -- they're thinking too much." Her campaign strategists? What about her? Dave says: "It seems to me that when your party's president shows up in your state, a gubernatorial candidate should just go stand with him, tell the crowd that he's great, and let him say the same thing about her. Nobody would hold that against Mary Burke." But do we hold it against her when she avoids him? It seems timid, at the very least, and, indeed, Dave proceeds to talk about her missing an opportunity to fire up "the base... especially African Americans."
Would the people in the middle really have held it against her if she'd stood with the President? Dave seems to think there was no risk, but Obama's Labor Day visit was quite union-oriented. He spoke on a stage where
the scenery was a lot of people in AFSCME t-shirts and at least one prominent blue fist t-shirt. I think Ms. Burke had something to worry about there, looking too connected to the public employee unions.
The Democratic Party's "base" here in Wisconsin may love
that visualization of our state as a blue fist, but I think it's offputting to those of us in the middle who see the value of peace and good order and who will probably determine the outcome of the election.
ADDED: I'm just now reading
Christian Schneider's piece and realizing that Mary Burke was present on the stage (of what was called "Laborfest") and that she departed at the point when Obama began speaking:
Burke's desire to avoid being photographed with the unpopular president is particularly comical, given that everyone knows that her jailbreak was entirely a product of campaign strategy....
Yet Burke's photo op had to be sacrificed at the altar of campaign "strategy."...
Burke wanted to avoid the visual of standing near Obama because she knows the picture would be run over and over to equate her politics with the president's....
[Burke] may even get the chance to dodge Obama again before the big election. The only question will be why he allows her to disrespect him so — if he comes back, he should jump into the background of every photo op in which she takes part. Call it the "Photobama."
AND: For the original post, I took my facts from Mayor Dave, who wrote: "Mary Burke, who attended the rally, did not appear on-stage with the president." Based on that, I speculated that she might not have liked the t-shirt scenery, especially the blue fist. But now I think I understand that she was on the stage and she ducked out specifically to avoid appearing
with Obama. That's really flagrant Obama-shunning, and I withdraw my speculation that she might have had the alternative motivation of wanting to avoid the appearance of too close an alliance with the public unions that Governor Walker is known for having tamed.