well, OMI, i agree insofar as i also don't care for or about Bar ... but she is becoming a proper celebrity. and whether it's because of her work or her boyfriend is irrelevant. from the editor's perspective, they see in terms of $$$. magazine sales have declined all across the board. the SI issue has lost so much of it's significance. they need to put someone on the cover that they can bank on, literally.
last year Marisa was the right choice because she was teetering right on the edge of become a very famous model. giving her the cover was mutually beneficial in that it helped her career in a major way, but also because she was already well-known she could do all the major events and the press would turn up for her. (*and i'm not even a fan of Marisa, so it's not a biased opinion*) i bet if we looked at the numbers, Marisa's was the best selling issue in years.
and because Bar is sort of on that same level -- right at the cusp of becoming VERY famous -- putting her on the cover should have a similar effect. and i suspect it will.
whereas Jessica - as gorgeous as she is - she isn't at the cusp anymore. this is the ONLY thing that is keeping her even remotely in the spotlight, at the moment. so to put her on the cover wouldn't stir up nearly the publicity (*and thus, magazine sales*) as Bar.