Well I can't speak for the reasons, but here are my guesses based on my observations:
One of the not-so-loudly-advertised, yet apparently evident, goals was to give a minor tweak downwards in dice pool sizes. You can see this across the board in numerous examples: Armor doesn't add to soak. "Average" in a stat is now 2 instead of 3. You're capped out at +4 bonus dice to any skill test. All of these sorts of things still doesn't stop you from being able to get 16-20 dice in a skill or two, but it does make it less "necessary" for you to do so. 12 dice counts for a little bit more than it did in 5e, since the NPCs all tend to have a slight nerf to their dice pools.
As for the viability of Attributes E pick, that's a recurring topic of discussion with varying views. I won't go into all mine, other than just to say "yeah, but at least 9 times out of 10 you probably REALLY ought to consider rethinking that choice." You'll need to hit some perfect storm/trifecta of using a big metatype pick, requiring lots of gear, and not really minding having bad physical stats. A Dwarf Technomancer who spends all his time in VR, has expensive drones/vehicles, and maybe uses lots of cyberware to augment his stats is the kind of build that can get by with Attributes E.