When the game started item duplicates were needed to upgrade them. 0.35 update Patch on May 2021 changed that and introduced relics. The reason was:
First all relics were set dependent (like current mythic relics) but that was also considered to be too tough on players so it changed into rare, epic and legendary relics being universal and only mythic relics remaining set dependent. And now we go back to “needing duplicates” for spells (spell pages) and for gear even worse since we no longer can evolve it. The changes are clearly designed to promote grinding and therefore spending money to shorten the times. The problem is that by making the game more grindy it is also becoming less casual friendly and more boring for those that aren’t either paying or hardcore farmers.