Just throwing something at the wall, with nothing but speculation on my part....
What it feels like to me, is that at least some (probably most?) of the early powerwall 2s (by early I mean through the end of about 2020 or midway through 2021) were probably manufactured with either the rated capacity (13.5kW in the US) or very very slightly more than that capacity.
It seems to me that at some point, Tesla decided to put an extra kW or so in them, and also likely tweaked the charging algorithms so that 100% charge isnt actually 100% of the capacity of the actual physical installed battery.
One could get really annoyed by this (and I wont blame anyone who does) but that type of thing is what the 10 year warranty is to protect against. I have proof myself that Tesla will eventually replace them under warranty (although it took a long time in my case, they had not quite hit the threshhold but had a noise issue Tesla could not resolve).
I believe Tesla also "could" replace these with remanufactured powerwalls, like they do with car batteries (I think their warranty might allow them to do this) but in my case mine were brand new powerwalls, still in the box, with the protective wrap still on (that I got to pull off myself this time, unlike when my original powerwalls were installed).
Its my belief that Tesla is going to end up replacing a larger percentage of the early installed PW2s but again that is just nothing but pure, 100% speculation on my part, with no data to back it up. Nothing more than a hunch.