having something that you can do, repeatedly, as often as you want during the week, that has a chance of rewarding a gear upgrade, no matter how slim the rng chances wind up being. is still better than not having -any- options for content to get gear upgrades at all.
prior to M+ once you were done with your raids for the week, that was it. if you got nothing, then you got -nothing- (because the vault didn’t exist yet either)
at least this way there is still something you -can- do to get upgrades.