Why don't astro cards stack?

[Seraphor]

Oh and as it seems I can post again:

Ironically, regens do stack, all of them.
WHM and AST, two WHMs, or two ASTs, you can stack all their regens.

Edit due to daily post limit:


No they do.
Shields don’t stack, but all regens do stack. Play dual Diurnal AST and you’ll see the two sets of Helios and two Benefics on your tank.

It's a shield thing, not a dual AST thing.