I think there are two reasons for that. One is the low resolution of bonuses in 4e – it's basically advantage or nothing (or sometimes an added die). And advantage is a pretty chonky bonus, so if you want advantage to be a rider on another ability, that ability has to be either very weak or highly limited. But at the same time, giving someone else advantage is generally not as good as what you could do yourself – at best it's a 50% increase in hit probability. There could be some room in setting someone up with advantage for use with a powerful but limited-use ability, but 5e doesn't have many of those that use attack rolls (I remember considering this for a wild mage, but pretty much all spells that deal decent damage use saves – and that's fair, because that generally means you don't waste a slot on a miss).
The other is that combat is usually over pretty fast in-game. Is spending an action and a 1st-level spell slot (and concentration) on giving allies +1d4 to hit with bless better than casting guiding bolt for 4d6 damage and giving an ally advantage on the next attack? Bless math gets wonky because of probabilities, but I figure it should be about a 10-20% increase in damage per target, so how many attacks do your party need to make to balance out the 4d6 damage + 50% boost to a single attack?