As far as I recall from a community league newsletter, when I lived there, Sunny is right that it's always been this way. The newsletter said that it used to be a subtle thing, before 114 widened so much and the lrt bisected the two parts of McKernan.
The reason the league wants to keep it, according to the newsletter, is that it's home to a lot of dense development, and they don't want to loss a not-insignificant chunk of their residents to Belgravia. According to
this city report, grants to community leagues are primarily distributed on a per capita basis, meaning the McKernan league has a financial incentive to keep this area under its purview.
Either way, it's an enticing pocket for them to keep, and they don't want to lose it just because of how the 114/lrt corridor developed.