I Don’t know why
The reason why some footprints are missing in the kicad library is explained in this FAQ article: Why a footprint points to a 3D model but the model file doesn't exist?
regarding your specific mentioned footprints:
- for the SOP IC: take the generic SOIC-8_3.9x4.9mm_P1.27mm.step ??
- for the others:
- look into the datasheet of the devices you want to use → determine manufacturer name and manufacturer part number
- look at the manufacturer website for a 3D model
- sometimes the bigger distributors (mouser/digikey/farnell/…) also offer 3D-model files
- look elsewhere on the internet, there are 3D-collection websites which have sometimes the needed models
- look through the 3D-models delivered with kicad - they are sorted by type. Sometimes a similar named 3D-model can be used