It exists for younger players.
My guess from a Developers' perspective, is that while you're young you use up your Credits on upgrading them. As your Toon gets stronger, you farm stronger Mods. Just like in other role playing video games, your Level 10 Warrior is fine with a Level 6 Sword. By the time you're Level 80, you should have gotten rid of it, and replaced it with a Level 70+ Sword with a fancier name.
Though it would make sense to not continually get 3-dot Mods in the final tier of the Challenge. Especially when a player has been Level 85 for months. Additionally, there should be some cut-off of when even the 4-dot Mod ceases to show up in the final tier. It's already difficult enough with the RNG determining when you get a good Mod.