My most charitable view is that Google have found a major fault with the Pixel 4a battery and want to mitigate a repeat of the Galaxy Note 7 without saying it outright and causing a panic.
My least charitable view (and immediate reaction) is that they're purposely ruining a viable budget phone to make more sales.
Either of these are terrible. At no point has Google came out and stated -why- they're pushing this update in the first place. And as someone who hasn't updated I'd really like to know if my phone presents an immediate threat (and I'm sure Governments and airlines would also like to know) before I remotely consider an update that'll practically destroy my device.
On top of this, within a day of being notified about this update, Google drastically raised the price of new Pixels on their store. Again if I'm charitable it could just be automatic global market price updates, but that goes out the window when Google must have prepared this update, FAQs, support plans, etc, then released it just before said price updates. The $100 discount recourse doesn't go far when the 8a jumped from £379 to £499. It's hard not to feel suspicious about it.
While I'm here, I did briefly write about my experiences with the 4a, though I'm far from a competent tech writer: https://callmeo.live/blog/ode-to-the-pixel-4a/