Having the files on your device only part of you control your data
Being able to use said data again is the other half of it 
Dillinger works fine because it’s markdown and the entire world has reimplemented markdown and fragmented it a billion times now.
KiCad is very niche in the broader world, sure there can be another kicad_pcb, kicad_sch supporting editor and there are right now ones that support it, but perhaps not always will be. Who knows what the future holds.
At least with KiCad you get this nice binary that’ll work until the end of human civilization on the OS+machine it originally did.