I both fix most things myself, but others I farm out like making & machining "new" parts.
I do not own a mill, metal lathe, and other machines including the tooling needed for those machines to make parts.
At my age, it is cheaper to pay someone to do the machining for me than try to acquire the necessary equipment to do the machining myself, and I could do it as I come from a family of skilled trade relatives which I have worked around for a number of years. This does help to define scope of work with less confusion.
And that does not take into account the space to house all of that equipment.