The issue is the devs obsession for accessibility, balance and casualism. Means that ultimately everything is incredibly forgiving. Which in turn is the biggest issue healers have.
Incoming damage is so firgiving that Shields are rarely necessary.not just shields but gcds in general. (Cant tell you the last time my scholar used psychic) Hell most of the time it's so forgiving tanks don't even "need" cooldowns.
The other problem with Shields. For scholar at least is there all gcd. Which means if you don't 100% know the script of a fight they're useless, as 95% of the time if you started casting Shields the instant you saw a bosses cast bar its already to late to shield the damage.