In previous posts you’ve told us that you have vast quantities of unused crafting materials precisely because you don’t make use of Cube recipes. So, of course your experience is that you don’t get primals via reforging but that’s because it’s a method you don’t use!
The Cube’s “Reforge legendary” is, by far, the single most reliable method of getting a specific item as a primal, regardless of whether that’s a method you use or not. I know you don’t like it when I mention maths, but it really comes down to that.
Primals are 1 in 400 legendaries.
When a mob drops a legendary, it can be any legendary in the game. Due to smart loot, 85% of those will be for the class you’re playing, 15% will be for other classes.
So, let’s say what you want is a specific primal mighty weapon for a Barb. When legendaries drop from random mobs, 85% of the items are picked from a loot pool of things a Barb could use. Let’s say, conservatively, that there are 150 possible items a Barb could use. That means it’s a 1 in 150 chance of being the weapon and, if it is, there’s a 1 in 400 chance of it being primal. That means it’s (1/150) * (1/400) = 1/60000 chance of being that primal weapon.
Okay, how about Kadala? Well, at least you could target it as “one handed weapons” but that might still have a pool of 20 weapons. So it’s (1/20) * (1/400) = 1/8000 chance of being that primal weapon.
Okay, what about “upgrade rare to legendary”? This cuts down the loot pool further, as it means you could just get mighty weapons rather than any one-handers, so let’s say it’s 1 in 10. That’s (1/10) * (1/400) = 1/4000 chance of being that primal weapon.
That brings us to “reforge legendary”. The result is always going to be the same item as you put in, just with randomised quality / affix values. That means it’s 1 in 400 of being primal. That’s 1/400 chance of being that primal weapon.