Situation is simple, like 5 cents - with resurrect being on crazy long cooldown(30 seconds is more than enough time for someone to screw up and die) Mercy relies mostly on heals(which aren’t that strong compared to other supports) and damage boost. Both of those require teammate, that is strong enough to survive with 60 hps and hits frequently enough for damage boost to work, while also having burst damage. Unsurprisingly, often it’s exactly 1 player from entire team, making pocketing inevitable.
I will always want AOE hide and rez, especially since it allows to compensate quality with quantity - resurrect more teammmates, if they are unable to win 1v1s. Pocketing is what you end up doing, if you just can’t resurrect teammates frequently enough.
Single resurrect reinforces pocketing, helping to maintain it by resurrecting “chosen one” on your team.