Why can't Manamune/Muramana have cooldown reduction like Archangel's Staff/Seraph's Embrace has?

One of the main reasons why any champion not named Ezreal does not build Manamune is because it lacks cooldown reduction.

Why it is important? One of the main reasons why Archangel's Staff used to be a very unpopular item before is because it had no cooldown reduction. This means that you would take too long to actually stack the item, because you couldn't spam your abilities as often. By the time you had enough cooldown reduction, the game was already over, and you didn't stacked it. Cooldown reduction is a very important powerspike for Tear users. Otherwise only a few champions bother purchasing it, because they have no other option (or in Ryze's case, because he scales with mana).

Adding cooldown reduction may not solve all of Manamune/Muramana problems, but would help making it a more viable option for other users. Switching the Pickaxe on its recipe with a Caulfield's Warhammer would even make its recipe better, since you are able to build Longswords (which helps when you are behind).

Another thing Riot could do is to get rid of the stacking on autos, and make Manamune/Muramana stack exclusively from spells. While most potential Manamune/Muramana users must auto for their damage, lets face it; they are mostly spell focused.

Without those changes, Ezreal may continue to be the only champion that build Manamune, and that is only because he doesn't have a better build path. If weren't for Ezreal, Manamune would be as purchased as Ohmwrecker is.