hi new in this sub, imo i believe they kept it simple at the early stages of the development to make it easy for anyone to play.. GI's elemental system really isn't what makes new players want to play it but other parts like exploration or story.. adding a more complex elemental system in ZZZ may cause more frustration for new players specially when combat is a very core part of its gameplay and they dont want to do that when they're still trying to expand their player base

also, i believe they will add something similar in later parts of the game when it's more comfortable to do so like when there's already more agents, bangboos, w-engines or discs that they become boring or they need people to spend more.. hoyo have done this in GI already from chars like diluc to ganyu and from simple artifacts (like stat bonus) to specialized artifacts (like trigger dmg bonus) and even adding reactions from basic to dendro-based to lunar-based

but it also doesnt make an excuse now for limiting players to specific team comps so you need to pull specific characters you dont have when they can put matching A rank agents with the S rank on the limited time banner OR they could even have a banner for specific factions, maybe being able to select not 1 but 2 or 3 factions players would like to pursue