Because they're boring. It's boring to play a cleric. Offensive debuffs have been nerfed into the Challenger Deep. That's why everyone decides to cast Spiritual Weapon and Spirit Guardians or Bless. They're the only above rate spells. Anything else you take is either so narrow that it's probably never going to come up on any given day, or is an under par damage spell, or is a healing spell, or is something with both concentration and saving throws. Oh, and Guidance. How compelling! Nobody finds the bag of infinite d4s annoying!
Other classes get cool things to do other than cast spells, or they're a Wizard and just have a better spell list. Not cleric. Cleric is boring. The spell list is overall narrow. The class abilities are overall narrow. The subclasses are interesting, but your 2nd level ability is always tied to turn undead, which you spend like 4 class levels upgrading to be better against chaff but the subclass alternative never improves. Your 8th level ability means you can spam cantrips better or just look really sad compared to Extra Attack. And divine intervention is so unreliable, and has such a high cooldown, and has such a nebulous benefit that it doesn't really count as an ability at all.