Advice request from mechanical engineers

[CADplans]

As far as why the recommended load is so low for rod, I think a major concern is notch toughness.

The simple design of threaded rod means the entire length is subjecting the rod to looking like it is notched.
A notched piece of steel is simply going to offer less strength than a smooth piece of steel.
The "notch", which in this case is the threads, causes localized stress risers to occur.

You calculate the stress based on the root diameter of the threaded rod, and come up with "X"

Then, when the notch raises the stress locally,, there is some design factor that will reduce "X".

Cheapo threaded rod looks like the threads were created with a dull hatchet.
The cracks at the root of the threads could not be worse.
So, also, since the cracks that are threads are so bad, the notch stress increase is maximized.

The cheapo threaded rod could be greatly strengthened by sand-blasting the root of the threads to eliminate all of the locations where the stress is increased.

The threads could be roll formed into the rod.

These things are not done,, the usable load of the rod is simply reduced.