Another factor is that, compared to the classical guitar and the flamenco guitar, the typical steel-string acoustic guitar has a very narrow string spacing, at the nut, at the bridge, and everywhere inbetween. This narrow string spacing is not sufficient to play the left-hand fingerings required of classical or flamenco guitar, and is not sufficient to enable your right-hand fingers to pluck the strings finger-style using the techniques that flamenco requires.
In short, a steel-string acoustic guitar is designed for an entirely different musical purpose, style of playing, and style of music than that of a classical or flamenco guitar. So if you want to play flamenco, you need a flamenco guitar, or for starters, a classical guitar.