The reason those things will be on one side and not the other probably has a lot to do with the assembly line when the trucks are manufactured. Somewhere along the line in the course of screwing something together the human that's doing the assembly gets close to, or has a history of bumping/scratching the top of the shock on that side, so the fix was determined to be a thread protector on that one. It could also be a case of threads getting damaged from something else as it's being put together.

Joe (former assembly line manager)