Given that shammie stat buffs increase the state caps by the appropriate amount, why is it that bard songs don't? For example, our lvl 109 War March songs increase STR by 293 but since most toons are already capped this is pointless. The equivalent Shammie buff also increases STR but raises the cap also so that the STR benefit is realized. Beastlords spells also increase the cap. Is there a reason why bard songs don't increase the cap?
If you're looking for a literal reason, those bard songs don't have a slot on the spell effect data specifying that the respective stat should have its cap increased. If you're asking why the spell dev hasn't added a slot to do so... well, the world may never know.
Yeah, the strength ultimately serves no purpose to anybody in level 110 gear. but they also can't just add a cap increase to it either because song modifiers, they'd have to rebalance it or it would add like 1200 strength lol.
The amount the cap is increased by is defined separately with its own calc, base, and max values. So even if the strength added was 1200, they could easily increase the cap by a much lower value if they desired.