Because alot of people are begging for it.

Realtime Filters, Realtime Blending Modes, Curve Animation Editor(property specific), cacheAsBitmap and Realtime bitmap manipulation, and a slew of other tweaks... to an animator this is the most significant update of Flash ever(or in a long time... I wasn't around with the first few version of Flash... so I can imagine an update that allowed animation at all was the most important update for an animator ) This isn't PowerPoint Transitions, this is more in line with After Effects made live.

If you weren't an animator, I would still think you'd be pretty pleased about the incredible performance spike provided with cacheAsBitmap, and some other features, such as the Browse feature?

If it's confusing, I'm sorry. But to those who get it, it's absolutely thrilling!