I love love love the story behind the Hesperos suit. Seriously good stuff!
One thing to bear in mind, when it comes to answering the question of "Why don't we hear more about these terraforming engines?" is that the vast majority of what we and the Vanguard now know of Venus during the Golden Age comes from the mission The Archive. At the end of that mission, we must protect our Ghost as they download the data from Dr. Shims main terminal within the Acadamy of the Ishtar Collective. The main focus, at that time, was the Vex. So it stands to reason that it would take some time for the Cryptarchs to begin researching any other findings from that mission. Keep in mind also that this armor was released a Playstation exclusive Legendary armor at the time of TTK.
As for why humanity had to further terraform Venus in the first place? Well, my very loose theory is that when the Traveler started the terraforming process on Venus, it came across the Vex (we know from our first mission on Venus that many of the structures found there pre-date humanity by centuries if I'm not mistaken) and fled. No, there is no proof of this, other than the fact that the Traveler did not stay and terraform it further. Humanity comes to Venus, later into the Golden Age, to find that the planet is only partial inhabitable. We take it upon ourselves to finish the job the Traveler started and find the Vex ourselves.
FInally, as for why we do not see these terraforming engines anywhere - well, from the flavor text of the armor itself, it states that these engines were placed deep underwater. And, if you look closely at the design of the armor itself, you will notice that it is modeled after deep water diving gear.
Awesome piece of item lore for which got me into item lore and trivia in the first place!