Not only is "Look Back at It" not what I'm thinking of with modal (as you're suggesting here), it has one of the most involved chord progressions I've heard in a hip-hop song in a while, going around the circle of fifths (technically going counter-clockwise, sort of, like a "circle of fourths" but that's too much of a digression for right now and I may be getting that wrong?) in a way that's reminiscent of a lot of disco music (I'm pretty sure it's the same chord progression as "I Will Survive").

Modal music is all about the notes in the scale and less about which notes you play based on a chord. Chords can change in modal music, but the important thing about it is that you maintain the integrity of the scale itself, and so a lot of modal music examples outside of jazz stay on a single chord and never change.

Think of the "Simpsons" theme, which gets a lot of mileage out of the Lydian mode. It stays on a single chord as that melody plays, and you can hear the distinctive note of the mode in the third note, which is the note that tells us that it's not just playing a major scale, even though the song "feels like" it's in a major key. You would play a C major chord, but you would sing a raised fourth, changing the mode of the song.

Rock and roll itself uses a pentatonic scale, but that scale is based around chord progressions -- specifically blues chord progressions.

The difference with current rap music is that the singers are singing the pentatonic scale on a single chord, playing with predictable notes but not singing any specific melody; they're using the mode to sing-rap, and can bounce up and down across the scale without worrying about hitting a bum note, since the chord will never change.

By contrast, you need to be very careful with the melody you use in "Look Back At It," because it's got a ton of chord changes, eight different chords in one cycle of the melody, so if you just tried to improvise in some mode, you would likely hit a note that didn't "fit" the chord you were playing. Modal music likes simple chords, something like that.

When you use a chord progression, the melody is in a careful dance with the chords you're playing. There are notes that fit in one chord but not in the other. On the flipside, there are notes you can sing in one chord that sound totally different -- even though you're singing the same note -- in the next chord. This is how confessional teenpop got its "wind beneath the wings," by hitting the fifth note in a minor key that became the major third when they went major (cf. "Into the Rush"). So you stay on the same note, but you transform a heavy minor note into an uplifting major one; that's the "lift."

By contrast, you don't need to worry about right and wrong notes when you're using a mode with a single chord. You can play any of the notes you like in any order and it sounds more or less OK. This is what I do with my kids on the piano -- I play a D-minor figure in the bass and just tell them to hit all of the white notes. They all sound good, because they're playing around on a Dorian scale. In hip-hop, rappers are playing around in an pentatonic scale, but it's still playing around; there's no wrong note.