and was largely kept a secret for the most part, except for some circles, because the above named planets did not market their primary planets properly
This "was kept a secret" gets passed along by people and it's embarrassing how no one that "pays it forward" puts 2 brain cells to work on it.
People knew and know about repeatable on attributes but like everything in the game it's not in the tutorials and this being a RCE, where it's mostly player versus player business (and not player vs MA despite what some may still think in loot 2.0), not everyone makes public tutorials and shares everything. Their hunting grounds would fill up past the point where it's usable.
So I would replace "this was kept a secret" with people not giving a fuck. There are probably still stamina repeatables on RT or other attributes but people don't care about attributes that much. Some do obviously, but for the most part these don't bring an important advantage. People farming for attributes most likely make an investment without a return. Maybe they'll be better in the future, but not so much now. People do have different goals in the game which is perfectly fine and while MA can maintain this strategy, they're golden.
This being kept a big secret is mostly because ignorance. Of players on one side as there are still players that don't care about efficiency, looter and learning the basics and on the other side it's well known ND's ignorance and also MA strategy was never to teach people what how to play.
Hunting before loot 2.0 with great gear, attributes rewards and skill rewards were just a small nice bonus.
General rule of thumb, before you pass along some information, before jumping into someone else's hate train, run the information through your personal filters first, see if it's BS or not because it's much easier to tell yourself "ahh, he must be doing some shit" instead of acknowledging someone's hard work and determination and make yourself work as hard towards your own goals.