D.C. and Baltimore are both predominantly black. Philadelphia is predominantly white (74%). Since blacks vote Dem about %90 it makes sense in those cities but not in Philadelphia. Agreed Philadelphia has a higher than average gay population, I doubt it tends towards about %50 which would be needed for it to account for a 4:1 ratio.
The 74% white figure is for the whole 13-county region. Philadelphia county is the same as Philadelphia city. You can look it up, but I am confident it is 50% or more non-White. If you compare the Philly figures to the CITIES of St. Louis, Baltimore, Chicago, Memphis, you will see comparable Dem percentages of the vote.