Difference in Sorcerer and Oracle

Why do wizards and sorcerers have a smaller attack and health bonus than oracles and pure priests?

Sorcerer and Mage lvl 20:
Attack roll: +10 +5 0 0
Sort By lvl: 1 = 6 - 2 = 6 - 3 = 6 - 4 = 6 - 5 = 6 - 7 = 6 - 8 = 6 - 9 = 4
HP per level = 4
Healing spell = none = support spell = good, Sort attack = Very Good

Oracle and priest level 20:
Attack roll: +15 +10 +5 0
Sort By lvl: 1 = 6 - 2 = 6 - 3 = 6 - 4 = 6 - 5 = 6 - 7 = 6 - 8 = 6 - 9 = 4
HP per level = 5
Healing spell = Very good = Support spell = very good, Sort attack = Good
More weapon choices
can wear light and medium armor
the Mystery and the curse

Clerics, oracles and druids are divine casters, not arcane. They usually built as semi combat more sturdy charachters with ability to spellcast, depending on a god/domain/mystery have somewhat diminished combat caster potential, but can became truly powerful in skilled hands as combatants or as casters.

Full arcane casters lack in physical department due to more broad spell access and can became truly devastating entities on they own, as pure classes with some exceptions not so good as usual combatants, their power lays in spells. Diminished bab scales with wide spectre of touch spells, which are easier to land on most enemies.