It's just a shift in cultural norms and what is acceptable in society. It isn't just found at Walt Disney World. It isn't a specific group of people, a specific word, or a specific event that cause such language. It just is more prevalent today just as much as females showing skin today compared back in 1914 or how rock n' roll music is ruining the fabric of the nation as it was in 1955 or how the Power Rangers are promoting violent crimes back in 1993. I was raised a sheltered child where about the only bad words I heard were "damn", "s**t", and "b***h" and those were extremely rare.
Things change and unfortunately, this seems to be one of them. You can place blame, preach the downfall of society, and relieve the golden years, but as with the other examples, this too will pass. Before you know it, these words will be so common and normal that they will lose their meaning as bad words and better described as words of frustration, excitement, or anger if it hasn't already started to morph into that already.
Even Disney admits to this in Carousel of Progress as we see clothing, gender roles, and respect for elders change through each act. The daughter in Act I is "indecent" and has to be home by 9pm and mother is busy doing all the housework, by Act IV she talks back to her parents, father is cooking while mother is programming the new oven, etc. Bad language is just one part of lower standards, less manners, and less civility we see all around us. I still doubt we'll ever see the day that Act IV is updated to reflect a future where bad words are spewed out even in the show script, but then again...will it ever even get an update at all.