Subdividing list with another list as a reference

Subdivide @@@ Partition[Flatten@Riffle[Partition[list1, 2, 1], div], 3]

or

Subdivide @@@ Flatten /@ Transpose[{Partition[list1, 2, 1], div}]

or

Subdivide @@@ Transpose@{list1[[;; -2]], list1[[2 ;;]], div}

or

Subdivide @@@ Transpose@{Most@list1, Rest@list1, div}

Can it be done shorter....

Another way:

MapThread[Subdivide, {Most@list1, Rest@list1, div}]

The answer you want can be reached this way:

list1=Partition[list1,2,1]
f=MapThread[Insert,{list1,div,Table[3,{Length[list1]}]}];
Apply[Subdivide,f[[#]]]&/@Range[Length[list1]]