As far as I understand harmony, the perfect 5th, being the note that adds the least color to a chord after the octave, doesn't do much to define the chord. That's why, when doing voice leading it's better to double the root or 3rd of the chord, which help reinforce the degree or character of the chord. In D Mayor, when you use the 2nd inversion of D (A D F#) it sounds closer to the V chord with its tensions (4th and 6th) than an inverted I chord. That's why playing bouncing bass works, it's kinda like doing a whole chord change just by moving one note.