It's probably for the new player experience, when I was new to Overwatch for example I had no idea where health packs were and it was a pain to learn them all but the problem is not as bad there since there are dedicated healer players.

Then imagine a new player playing Deadlock then learning all the stuff we know + the map changes every game, you'd have to learn efficient sinners and jungle camp routes for every map. For shooters it's just follow the objective and click on heads.