Increasingly better gear has issues, obvious ones really. If you increase gear performance by even a relatively minor percentage per update, let's say, oh, 5-6%, by now you'd have gear that was almost twice as good as what existed a couple years ago. So, the Adaberk equivalent would be the norm, and the New Adaberk would be +20/+30. Any content designed around the original set would be invalidated by the following sets after a while. By definition making better gear in each update would make the previous updates worthless, there's nothing else it can do. You may keep some of your players longer, but only by putting them on an endless gear treadmill, locked in a cycle whereupon they can never stop trying to get the next piece of "best" gear.
Weapons obviously have an established "best", namely relic weapons, which is a good indicator of what SE considers the maximum allowable. Thing is, the edge isn't that enormous between a Relic and a really good weapon that's already out. Even minor improvements in weapons would quickly eclipse the relics.
So SE has chosen to define what they consider their maximum, and instead of continually increasing it, rather offer a variety of options as to how to achieve it, and a variety of approaches to acquire it. Rather than try for an E.Body, you can now try for a Shadow Breastplate, or an Ares Cuirass, and so on. They're not any easier to acquire (and in both cases are stupidly expensive to make), but it's an option that can be scheduled at the very least.