the problem with slap is about hand anatomy. when you slap with your thumb your fingers are naturally in a place ready to pluck the strings under the string you slapped, so its very tricky to play lines in a single string, and is practically imposible to slap a high note and pluck a low note. Thats the reason why 90% of the slap lines are root note + octave or root note + 7th or 6th. So, if your main weapon is slapping you become repetitive sooner or later...
If you practice you can slap and pop on the same string quite easily. But it is almost impossible to slap a high string then pop a low one. But, I think the repetitive nature of slap bass lines is more lazy composition. Just like any style can become repetitive.
